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Apache Cassandra™ 2.1Documentation

February 17, 2015

© 2015 DataStax. All rights reserved.

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Contents

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Contents

About Apache Cassandra............................................................................................... 8

What's new in Cassandra 2.1.........................................................................................9

CQL..................................................................................................................................10

Understanding the architecture................................................................................... 11Architecture in brief........................................................................................................................... 11Internode communications (gossip).................................................................................................. 13

Failure detection and recovery...............................................................................................13Data distribution and replication........................................................................................................14

Consistent hashing................................................................................................................. 14Virtual nodes...........................................................................................................................15Data replication.......................................................................................................................16

Partitioners.........................................................................................................................................17Murmur3Partitioner..................................................................................................................18RandomPartitioner.................................................................................................................. 18ByteOrderedPartitioner........................................................................................................... 18

Snitches............................................................................................................................................. 19Dynamic snitching...................................................................................................................19SimpleSnitch........................................................................................................................... 19RackInferringSnitch.................................................................................................................19PropertyFileSnitch...................................................................................................................20GossipingPropertyFileSnitch...................................................................................................20EC2Snitch............................................................................................................................... 21EC2MultiRegionSnitch............................................................................................................ 22GoogleCloudSnitch................................................................................................................. 23CloudstackSnitch.................................................................................................................... 23

Client requests...................................................................................................................................23

Planning a cluster deployment.................................................................................... 24Selecting hardware for enterprise implementations..........................................................................24Planning an Amazon EC2 cluster.....................................................................................................26Calculating usable disk capacity....................................................................................................... 27Calculating user data size.................................................................................................................28Anti-patterns in Cassandra................................................................................................................29

Installing..........................................................................................................................32Installing on RHEL-based systems................................................................................................... 32Installing on Debian-based systems................................................................................................. 33Installing the binary tarball................................................................................................................ 34Installing on Windows systems......................................................................................................... 35Installing on cloud providers............................................................................................................. 35

Installing on Amazon EC2......................................................................................................35Installing on GoGrid................................................................................................................42

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Installing Oracle JRE.........................................................................................................................44Installing the JRE on RHEL-based systems.......................................................................... 44Installing the JRE on Debian-based systems........................................................................ 45

Recommended production settings...................................................................................................46

Initializing a cluster....................................................................................................... 49Initializing a multiple node cluster (single data center).....................................................................49Initializing a multiple node cluster (multiple data centers)................................................................ 51

Security........................................................................................................................... 55Securing Cassandra.......................................................................................................................... 55SSL encryption.................................................................................................................................. 55

Client-to-node encryption........................................................................................................55Node-to-node encryption........................................................................................................ 56Using cqlsh with SSL encryption............................................................................................56Preparing server certificates...................................................................................................57

Internal authentication....................................................................................................................... 58Internal authentication............................................................................................................ 58Configuring authentication...................................................................................................... 58Logging in using cqlsh............................................................................................................59

Internal authorization......................................................................................................................... 60Object permissions................................................................................................................. 60Configuring internal authorization...........................................................................................60

Configuring firewall port access........................................................................................................ 61

Database internals......................................................................................................... 62Storage engine.................................................................................................................................. 62Separate table directories................................................................................................................. 62Cassandra storage basics.................................................................................................................62

The write path to compaction.................................................................................................62How Cassandra stores indexes............................................................................................. 65About index updates...............................................................................................................65

The write path of an update............................................................................................................. 65About deletes.....................................................................................................................................66About hinted handoff writes.............................................................................................................. 66About reads....................................................................................................................................... 68

How off-heap components affect reads................................................................................. 69Reading from a partition.........................................................................................................70How write patterns affect reads............................................................................................. 70How the row cache affects reads.......................................................................................... 70

About transactions and concurrency control.....................................................................................70Lightweight transactions......................................................................................................... 71Atomicity..................................................................................................................................71Consistency.............................................................................................................................72Isolation...................................................................................................................................72Durability................................................................................................................................. 72

About data consistency..................................................................................................................... 73Configuring data consistency................................................................................................. 73Read requests........................................................................................................................ 77Write requests.........................................................................................................................81

Configuration..................................................................................................................83The cassandra.yaml configuration file...............................................................................................83

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Configuring gossip settings............................................................................................................... 99Configuring the heap dump directory..............................................................................................100Generating tokens........................................................................................................................... 100Configuring virtual nodes.................................................................................................................101

Enabling virtual nodes on a new cluster.............................................................................. 101Enabling virtual nodes on an existing production cluster..................................................... 101

Configuring logging..........................................................................................................................102Commit log archive configuration....................................................................................................104Hadoop support............................................................................................................................... 105

Operations.................................................................................................................... 107Monitoring Cassandra..................................................................................................................... 107

Monitoring a Cassandra cluster............................................................................................107Tuning Bloom filters........................................................................................................................ 112Data caching....................................................................................................................................112

Configuring data caches.......................................................................................................112Monitoring and adjusting caching.........................................................................................115

Configuring memtable throughput................................................................................................... 115Configuring compaction...................................................................................................................115Compression....................................................................................................................................116

When to compress data....................................................................................................... 116Configuring compression...................................................................................................... 117

Testing compaction and compression.............................................................................................118Tuning Java resources....................................................................................................................118Purging gossip state on a node......................................................................................................120Repairing nodes.............................................................................................................................. 121Adding or removing nodes, data centers, or clusters..................................................................... 125

Adding nodes to an existing cluster..................................................................................... 125Adding a data center to a cluster.........................................................................................126Replacing a dead node or dead seed node........................................................................ 127Replacing a running node.................................................................................................... 128Decommissioning a data center...........................................................................................129Removing a node................................................................................................................. 129Switching snitches................................................................................................................ 130Edge cases for transitioning or migrating a cluster..............................................................131

Backing up and restoring data.................................................................................. 132Taking a snapshot...........................................................................................................................132Deleting snapshot files.................................................................................................................... 133Enabling incremental backups........................................................................................................ 133Restoring from a Snapshot............................................................................................................. 133

Node restart method.............................................................................................................134Restoring a snapshot into a new cluster........................................................................................ 135

Cassandra tools........................................................................................................... 136The nodetool utility.......................................................................................................................... 136

cfhistograms..........................................................................................................................136cfstats....................................................................................................................................137cleanup..................................................................................................................................142clearsnapshot........................................................................................................................143compact.................................................................................................................................144compactionhistory................................................................................................................. 144compactionstats.................................................................................................................... 146

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decommission....................................................................................................................... 147describecluster...................................................................................................................... 148describering...........................................................................................................................148disableautocompaction......................................................................................................... 150disablebackup....................................................................................................................... 150disablebinary......................................................................................................................... 151disablegossip........................................................................................................................ 151disablehandoff.......................................................................................................................152disablethrift............................................................................................................................152drain...................................................................................................................................... 152enableautocompaction.......................................................................................................... 153enablebackup........................................................................................................................153enablebinary..........................................................................................................................154enablegossip......................................................................................................................... 154enablehandoff....................................................................................................................... 155enablethrift............................................................................................................................ 155flush.......................................................................................................................................156getcompactionthreshold........................................................................................................ 156getendpoints..........................................................................................................................157getlogginglevels.................................................................................................................... 157getsstables............................................................................................................................ 158getstreamthroughput............................................................................................................. 158gossipinfo.............................................................................................................................. 159help....................................................................................................................................... 159info........................................................................................................................................ 160invalidatekeycache................................................................................................................160invalidaterowcache................................................................................................................161join.........................................................................................................................................161listsnapshots......................................................................................................................... 162move..................................................................................................................................... 162netstats..................................................................................................................................163pausehandoff........................................................................................................................ 164proxyhistograms....................................................................................................................164rangekeysample....................................................................................................................165rebuild................................................................................................................................... 166rebuild_index.........................................................................................................................166refresh................................................................................................................................... 167reloadtriggers........................................................................................................................ 167removenode.......................................................................................................................... 168repair..................................................................................................................................... 169resetlocalschema.................................................................................................................. 171resumehandoff...................................................................................................................... 171ring........................................................................................................................................ 172scrub..................................................................................................................................... 173setcachecapacity...................................................................................................................174setcachekeystosave..............................................................................................................174setcompactionthreshold........................................................................................................ 175setcompactionthroughput......................................................................................................176sethintedhandoffthrottlekb.....................................................................................................176setlogginglevel...................................................................................................................... 177setstreamthroughput............................................................................................................. 178settraceprobability................................................................................................................. 178snapshot................................................................................................................................179status.....................................................................................................................................181statusbinary...........................................................................................................................182statusthrift..............................................................................................................................183

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stop....................................................................................................................................... 183stopdaemon.......................................................................................................................... 184tpstats....................................................................................................................................184truncatehints..........................................................................................................................186upgradesstables....................................................................................................................187version...................................................................................................................................187

Cassandra bulk loader (sstableloader)........................................................................................... 188The cassandra utility....................................................................................................................... 190The cassandra-stress tool...............................................................................................................193

Using the Daemon Mode..................................................................................................... 196Interpreting the output of cassandra-stress..........................................................................197

The sstablescrub utility....................................................................................................................197The sstablesplit utility...................................................................................................................... 198The sstablekeys utility..................................................................................................................... 198The sstableupgrade tool..................................................................................................................199

References.................................................................................................................... 200Starting and stopping Cassandra....................................................................................................200

Starting Cassandra as a service.......................................................................................... 200Starting Cassandra as a stand-alone process..................................................................... 200Stopping Cassandra as a service........................................................................................ 200Stopping Cassandra as a stand-alone process................................................................... 200Clearing the data as a service............................................................................................. 201Clearing the data as a stand-alone process........................................................................ 201

Install locations................................................................................................................................ 201Tarball installation directories............................................................................................... 201Package installation directories............................................................................................ 202

Cassandra include file.....................................................................................................................203Cassandra-CLI utility (deprecated)..................................................................................................203

Table attributes..................................................................................................................... 204

Moving data to/from other databases....................................................................... 207

Troubleshooting........................................................................................................... 208Peculiar Linux kernel performance problem on NUMA systems.....................................................208Reads are getting slower while writes are still fast.........................................................................208Nodes seem to freeze after some period of time........................................................................... 208Nodes are dying with OOM errors..................................................................................................209Nodetool or JMX connections failing on remote nodes.................................................................. 209Handling schema disagreements.................................................................................................... 209View of ring differs between some nodes.......................................................................................210Java reports an error saying there are too many open files...........................................................210Insufficient user resource limits errors............................................................................................ 210Cannot initialize class org.xerial.snappy.Snappy............................................................................ 211Firewall idle connection timeout causing nodes to lose communication.........................................212

Release notes...............................................................................................................214

Using the docs.............................................................................................................216

About Apache Cassandra

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About Apache Cassandra

Documentation for developers and administrators on installing, configuring, and using the features andcapabilities of Apache Cassandra scalable open source NoSQL database.

Apache Cassandra™ is a massively scalable open source NoSQL database. Cassandra is perfectfor managing large amounts of data across multiple data centers and the cloud. Cassandra deliverscontinuous availability, linear scalability, and operational simplicity across many commodity servers with nosingle point of failure, along with a powerful data model designed for maximum flexibility and fast responsetimes.

How does Cassandra work?

Cassandra has a “masterless” architecture, meaning all nodes are the same. Cassandra providesautomatic data distribution across all nodes that participate in a “ring” or database cluster. There is nothingprogrammatic that a developer or administrator needs to do or code to distribute data across a clusterbecause data is transparently partitioned across all nodes in a cluster.

Cassandra also provides customizable replication, storing redundant copies of data across nodes thatparticipate in a Cassandra ring. If any node in a cluster goes down, one or more copies of that node’s datais still available on other machines in the cluster. Replication can be configured to work across one datacenter, many data centers, and multiple cloud availability zones.

Cassandra supplies linear scalability, meaning that capacity may be easily added simply by adding newnodes online. For example, if 2 nodes can handle 100,000 operations per second, 4 nodes will support200,000 operations/sec and 8 nodes will tackle 400,000 operations/sec:

To gain an understanding of Cassandra's origins and evolution, see "Facebook’s Cassandra paper,annotated and compared to Apache Cassandra 2.0", by project chair Jonathan Ellis.

/documentation/articles/cassandra/cassandrathenandnow.html

/documentation/articles/cassandra/cassandrathenandnow.html

What's new in Cassandra 2.1

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What's new in Cassandra 2.1

New features:

• User-defined types• Collection indexes• Better implementation of counters that makes them safer, simpler, and typically faster• New listsnapshots and reloadtriggers nodetool commands• Improved metrics reporting through the use of the metrics-core library

Performance improvements:

• Faster reads and writes than previous releases• Improved row cache• Reduced heap used by memtables• New counters implementation

Compaction and repair improvements:

• Post-compaction read performance• A configurable percentage of cold SSTables can be ignored• Incremental node repair

Other notable changes:

• Improved Hadoop support• Unique table IDs• Improved logging using logback• New configuration options for allocating and managing memtable memory• Improvements to bootstrapping a node that ensure data consistency• Bundled JNA• A number of other CQL and cqlsh changes

Release notes cover key changes in Cassandra 2.1. For a detailed list of changes, see the change log.

/documentation/cql/3.1/cql/cql_reference/cqlRefUDType.html

/documentation/cql/3.1/cql/ddl/ddlIndexColl.html

http://www.datastax.com/dev/blog/whats-new-in-cassandra-2-1-a-better-implementation-of-counters

http://www.datastax.com/dev/blog/cassandra-2-1-now-over-50-faster

http://www.datastax.com/dev/blog/off-heap-memtables-in-Cassandra-2-1

http://www.datastax.com/dev/blog/whats-new-in-cassandra-2-1-a-better-implementation-of-counters

/documentation/cql/3.1/cql/cql_intro_c.html

/documentation/cassandra/2.1/cassandra/releaseNotes.html

https://github.com/apache/cassandra/blob/cassandra-2.1/CHANGES.txt

CQL

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CQL

Cassandra Query Language (CQL) is the default and primary interface into the Cassandra DBMS. UsingCQL is similar to using SQL (Structured Query Language). CQL and SQL share the same abstract ideaof a table constructed of columns and rows. The main difference from SQL is that Cassandra does notsupport joins or subqueries. Instead, Cassandra emphasizes denormalization through CQL features likecollections and clustering specified at the schema level.

CQL is the recommended way to interact with Cassandra. Performance and the simplicity of reading andusing CQL is an advantage of modern Cassandra over older Cassandra APIs.

The CQL documentation contains a data modeling section, examples, and command reference. The cqlshutility for using CQL interactively on the command line is also covered.

/documentation/cql/3.1/cql/ddl/ddl_intro_c.html

/documentation/cql/3.1/index.html

/documentation/cql/3.1/cql/cql_reference/cqlsh.html


Understanding the architecture

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Architecture in brief

Cassandra is designed to handle big data workloads across multiple nodes with no single point of failure.Its architecture is based on the understanding that system and hardware failures can and do occur.Cassandra addresses the problem of failures by employing a peer-to-peer distributed system acrosshomogeneous nodes where data is distributed among all nodes in the cluster. Each node exchangesinformation across the cluster every second. A sequentially written commit log on each node captureswrite activity to ensure data durability. Data is then indexed and written to an in-memory structure, calleda memtable, which resembles a write-back cache. Once the memory structure is full, the data is written todisk in an SSTable data file. All writes are automatically partitioned and replicated throughout the cluster.Using a process called compaction Cassandra periodically consolidates SSTables, discarding obsoletedata and tombstones (an indicator that data was deleted).

Cassandra is a row-oriented database. Cassandra's architecture allows any authorized user to connectto any node in any data center and access data using the CQL language. For ease of use, CQL usesa similar syntax to SQL. From the CQL perspective the database consists of tables. Typically, a clusterhas one keyspace per application. Developers can access CQL through cqlsh as well as via drivers forapplication languages.

Client read or write requests can be sent to any node in the cluster. When a client connects to a node witha request, that node serves as the coordinator for that particular client operation. The coordinator acts asa proxy between the client application and the nodes that own the data being requested. The coordinatordetermines which nodes in the ring should get the request based on how the cluster is configured. Formore information, see Client requests.

Key structures

• Node

Where you store your data. It is the basic infrastructure component of Cassandra.• Data center

A collection of related nodes. A data center can be a physical data center or virtual data center.Different workloads should use separate data centers, either physical or virtual. Replication is set bydata center. Using separate data centers prevents Cassandra transactions from being impacted byother workloads and keeps requests close to each other for lower latency. Depending on the replicationfactor, data can be written to multiple data centers. However, data centers should never span physicallocations.

• Cluster

A cluster contains one or more data centers. It can span physical locations.• Commit log

All data is written first to the commit log for durability. After all its data has been flushed to SSTables, itcan be archived, deleted, or recycled.

• Table

A collection of ordered columns fetched by row. A row consists of columns and have a primary key. Thefirst part of the key is a column name.

• SSTable

/documentation/cql/3.1/cql/cql_reference/tabProp.html?scroll=tabProp__moreCompaction


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A sorted string table (SSTable) is an immutable data file to which Cassandra writes memtablesperiodically. SSTables are append only and stored on disk sequentially and maintained for eachCassandra table.

Key components for configuring Cassandra

• Gossip

A peer-to-peer communication protocol to discover and share location and state information about theother nodes in a Cassandra cluster. Gossip information is also persisted locally by each node to useimmediately when a node restarts.

• Partitioner

A partitioner determines how to distribute the data across the nodes in the cluster and which node toplace the first copy of data on. Basically, a partitioner is a hash function for computing the token of apartition key. Each row of data is uniquely identified by a partition key and distributed across the clusterby the value of the token. The Murmur3Partitioner is the default partitioning strategy for new Cassandraclusters and the right choice for new clusters in almost all cases.

You must set the partitioner and assign the node a num_tokens value for each node. The numberof tokens you assign depends on the hardware capabilities of the system. If not using virtual nodes(vnodes), use the initial_token setting instead.

• Replication factor

The total number of replicas across the cluster. A replication factor of 1 means that there is only onecopy of each row on one node. A replication factor of 2 means two copies of each row, where eachcopy is on a different node. All replicas are equally important; there is no primary or master replica.You define the replication factor for each data center. Generally you should set the replication strategygreater than one, but no more than the number of nodes in the cluster.

• Replica placement strategy

Cassandra stores copies (replicas) of data on multiple nodes to ensure reliability and fault tolerance.A replication strategy determines which nodes to place replicas on. The first replica of data is simplythe first copy; it is not unique in any sense. The NetworkTopologyStrategy is highly recommended formost deployments because it is much easier to expand to multiple data centers when required by futureexpansion.

When creating a keyspace, you must define the replica placement strategy and the number of replicasyou want.

• Snitch

A snitch defines groups of machines into data centers and racks (the topology) that the replicationstrategy uses to place replicas.

You must configure a snitch when you create a cluster. All snitches use a dynamic snitch layer,which monitors performance and chooses the best replica for reading. It is enabled by default andrecommended for use in most deployments. Configure dynamic snitch thresholds for each node in thecassandra.yaml configuration file.

The default SimpleSnitch does not recognize data center or rack information. Use it for single-datacenter deployments or single-zone in public clouds. The GossipingPropertyFileSnitch is recommendedfor production. It defines a node's data center and rack and uses gossip for propagating this informationto other nodes.

• The cassandra.yaml configuration file

The main configuration file for setting the initialization properties for a cluster, caching parameters fortables, properties for tuning and resource utilization, timeout settings, client connections, backups, andsecurity.

By default, a node is configured to store the data it manages in a directory set in the cassandra.yamlfile.


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• Package installations: /var/lib/cassandra• Tarball installations: install_location/data/data

In a production cluster deployment, you can change the commitlog-directory to a different disk drivefrom the data_file_directories.

• System keyspace table properties

You set storage configuration attributes on a per-keyspace or per-table basis programmatically or usinga client application, such as CQL.

Internode communications (gossip)Cassandra uses a protocol called gossip to discover location and state information about the other nodesparticipating in a Cassandra cluster.

Gossip is a peer-to-peer communication protocol in which nodes periodically exchange state informationabout themselves and about other nodes they know about. The gossip process runs every second andexchanges state messages with up to three other nodes in the cluster. The nodes exchange informationabout themselves and about the other nodes that they have gossiped about, so all nodes quickly learnabout all other nodes in the cluster. A gossip message has a version associated with it, so that during agossip exchange, older information is overwritten with the most current state for a particular node.

To prevent partitions in gossip communications, use the same list of seed nodes for all nodes in a cluster.This is most critical the first time a node starts up. By default, a node remembers other nodes it hasgossiped with between subsequent restarts. The seed node designation has no purpose other thanbootstrapping the gossip process for new nodes joining the cluster. Seed nodes are not a single pointof failure, nor do they have any other special purpose in cluster operations beyond the bootstrapping ofnodes.

Attention: In multiple data-center clusters, the seed list should include at least one node from eachdata center (replication group). More than a single seed node per data center is recommended forfault tolerance. Otherwise, gossip has to communicate with another data center when bootstrappinga node. Making every node a seed node is not recommended because of increased maintenanceand reduced performance.

Failure detection and recovery

Failure detection is a method for locally determining from gossip state and history if another node in thesystem is up or down. Cassandra uses this information to avoid routing client requests to unreachablenodes whenever possible. (Cassandra can also avoid routing requests to nodes that are alive, butperforming poorly, through the dynamic snitch.)

The gossip process tracks state from other nodes both directly (nodes gossiping directly to it) and indirectly(nodes communicated about secondhand, thirdhand, and so on). Rather than have a fixed thresholdfor marking failing nodes, Cassandra uses an accrual detection mechanism to calculate a per-nodethreshold that takes into account network performance, workload, and historical conditions. During gossipexchanges, every node maintains a sliding window of inter-arrival times of gossip messages from othernodes in the cluster. Configuring the phi_convict_threshold property adjusts the sensitivity of the failuredetector. Lower values increase the likelihood that an unresponsive node will be marked as down, whilehigher values decrease the likelihood that transient failures causing node failure. Use the default valuefor most situations, but increase it to 10 or 12 for Amazon EC2 (due to frequently enountered networkcongestion). In unstable network environments (such as EC2 at times), raising the value to 10 or 12 helpsprevent false failures. Values higher than 12 and lower than 5 are not recommended.

Node failures can result from various causes such as hardware failures and network outages. Nodeoutages are often transient but can last for extended periods. Because a node outage rarely signifies apermanent departure from the cluster it does not automatically result in permanent removal of the nodefrom the ring. Other nodes will periodically try to re-establish contact with failed nodes to see if they are

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back up. To permanently change a node's membership in a cluster, administrators must explicitly add orremove nodes from a Cassandra cluster using the nodetool utility or OpsCenter.

When a node comes back online after an outage, it may have missed writes for the replica datait maintains. Once the failure detector marks a node as down, missed writes are stored by otherreplicas for a period of time providing hinted handoff is enabled. If a node is down for longer thanmax_hint_window_in_ms (3 hours by default), hints are no longer saved. Nodes that die may have storedundelivered hints. Run a repair after recovering a node that has been down for an extended period.Moreover, you should routinely run nodetool repair on all nodes to ensure they have consistent data.

For more explanation about hint storage, see Modern hinted handoff.

Data distribution and replication

In Cassandra, data distribution and replication go together. Data is organized by table and identified by aprimary key, which determines which node the data is stored on. Replicas are copies of rows. When data isfirst written, it is also referred to as a replica.

Factors influencing replication include:

• Virtual nodes: assigns data ownership to physical machines.• Partitioner: partitions the data across the cluster.• Replication strategy: determines the replicas for each row of data.• Snitch: defines the topology information that the replication strategy uses to place replicas.

Consistent hashingConsistent hashing allows distributing data across a cluster which minimizes reorganization when nodesare added or removed.

Consistent hashing partitions data based on the partition key. (For an explanation of partition keys andprimary keys, see the Data modeling example in CQL for Cassandra 2.0.)

For example, if you have the following data:

name age car gender

jim 36 camaro M

carol 37 bmw F

johnny 12 M

suzy 10 F

Cassandra assigns a hash value to each partition key:

Partition key Murmur3 hash value

jim -2245462676723223822

carol 7723358927203680754

johnny -6723372854036780875

suzy 1168604627387940318

Each node in the cluster is responsible for a range of data based on the hash value:

http://www.datastax.com/dev/blog/modern-hinted-handoff



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Hash values in a 4 node cluster

Data Center Alpha

A

B

C

D

4611686018427387904to

9223372036854775807

- 4611686018427387904to- 1

- 1to

4611686018427387903

- 9223372036854775808to

- 4611686018427387903

Cassandra places the data on each node according to the value of the partition key and the range thatthe node is responsible for. For example, in a four node cluster, the data in this example is distributed asfollows:

Node Start range End range Partitionkey

Hash value

A -9223372036854775808 -4611686018427387903 johnny -6723372854036780875

B -4611686018427387904 -1 jim -2245462676723223822

C 0 4611686018427387903 suzy 1168604627387940318

D 4611686018427387904 9223372036854775807 carol 7723358927203680754

Virtual nodesOverview of virtual nodes (vnodes).

Vnodes simplify many tasks in Cassandra:

• You no longer have to calculate and assign tokens to each node.• Rebalancing a cluster is no longer necessary when adding or removing nodes. When a node joins the

cluster, it assumes responsibility for an even portion of data from the other nodes in the cluster. If anode fails, the load is spread evenly across other nodes in the cluster.

• Rebuilding a dead node is faster because it involves every other node in the cluster.• Improves the use of heterogeneous machines in a cluster. You can assign a proportional number of

vnodes to smaller and larger machines.

For more information, see the article Virtual nodes in Cassandra 1.2 and Enabling virtual nodes on anexisting production cluster.

How data is distributed across a cluster (using virtual nodes)

Prior to version 1.2, you had to calculate and assign a single token to each node in a cluster. Each tokendetermined the node's position in the ring and its portion of data according to its hash value. Starting inversion 1.2, Cassandra allows many tokens per node. The new paradigm is called virtual nodes (vnodes).Vnodes allow each node to own a large number of small partition ranges distributed throughout the cluster.Vnodes also use consistent hashing to distribute data but using them doesn't require token generation andassignment.

http://www.datastax.com/dev/blog/virtual-nodes-in-cassandra-1-2

http://www.datastax.com/docs/1.1/initialize/token_generation


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Figure 1: Virtual vs single-token architecture

The top portion of the graphic shows a cluster without vnodes. In this paradigm, each node is assigneda single token that represents a location in the ring. Each node stores data determined by mapping thepartition key to a token value within a range from the previous node to its assigned value. Each node alsocontains copies of each row from other nodes in the cluster. For example, range E replicates to nodes 5, 6,and 1. Notice that a node owns exactly one contiguous partition range in the ring space.

The bottom portion of the graphic shows a ring with vnodes. Within a cluster, virtual nodes are randomlyselected and non-contiguous. The placement of a row is determined by the hash of the partition key withinmany smaller partition ranges belonging to each node.

Data replicationCassandra stores replicas on multiple nodes to ensure reliability and fault tolerance. A replication strategydetermines the nodes where replicas are placed.

The total number of replicas across the cluster is referred to as the replication factor. A replication factor of1 means that there is only one copy of each row on one node. A replication factor of 2 means two copiesof each row, where each copy is on a different node. All replicas are equally important; there is no primaryor master replica. As a general rule, the replication factor should not exceed the number of nodes in thecluster. However, you can increase the replication factor and then add the desired number of nodes later.

Two replication strategies are available:

• SimpleStrategy: Use for a single data center only. If you ever intend more than one data center, usethe NetworkTopologyStrategy.

• NetworkTopologyStrategy: Highly recommended for most deployments because it is much easierto expand to multiple data centers when required by future expansion.

SimpleStrategy


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Use only for a single data center. SimpleStrategy places the first replica on a node determined bythe partitioner. Additional replicas are placed on the next nodes clockwise in the ring without consideringtopology (rack or data center location).

NetworkTopologyStrategy

Use NetworkTopologyStrategy when you have (or plan to have) your cluster deployed across multipledata centers. This strategy specify how many replicas you want in each data center.

NetworkTopologyStrategy places replicas in the same data center by walking the ring clockwise untilreaching the first node in another rack. NetworkTopologyStrategy attempts to place replicas on distinctracks because nodes in the same rack (or similar physical grouping) often fail at the same time due topower, cooling, or network issues.

When deciding how many replicas to configure in each data center, the two primary considerations are (1)being able to satisfy reads locally, without incurring cross data-center latency, and (2) failure scenarios. Thetwo most common ways to configure multiple data center clusters are:

• Two replicas in each data center: This configuration tolerates the failure of a single node per replicationgroup and still allows local reads at a consistency level of ONE.

• Three replicas in each data center: This configuration tolerates either the failure of a one node perreplication group at a strong consistency level of LOCAL_QUORUM or multiple node failures per datacenter using consistency level ONE.

Asymmetrical replication groupings are also possible. For example, you can have three replicas in one datacenter to serve real-time application requests and use a single replica elsewhere for running analytics.

Choosing keyspace replication options

To set the replication strategy for a keyspace, see CREATE KEYSPACE.

When you use NetworkToplogyStrategy, during creation of the keyspace, you use the data centernames defined for the snitch used by the cluster. To place replicas in the correct location, Cassandrarequires a keyspace definition that uses the snitch-configured data center names. For example, if thecluster uses the PropertyFileSnitch, create the keyspace using the user-defined data center and racknames in the cassandra-topologies.properties file. If the cluster uses the EC2Snitch, create thekeyspace using EC2 data center and rack names.

PartitionersA partitioner determines how data is distributed across the nodes in the cluster (including replicas).Basically, a partitioner is a function for deriving a token representing a row from its partion key, typically byhashing. Each row of data is then distributed across the cluster by the value of the token.

Both the Murmur3Partitioner and RandomPartitioner use tokens to help assign equal portionsof data to each node and evenly distribute data from all the tables throughout the ring or other grouping,such as a keyspace. This is true even if the tables use different partition keys, such as usernames ortimestamps. Moreover, the read and write requests to the cluster are also evenly distributed and loadbalancing is simplified because each part of the hash range receives an equal number of rows on average.For more detailed information, see Consistent hashing.

Cassandra offers the following partitioners:

• Murmur3Partitioner (default): uniformly distributes data across the cluster based on MurmurHashhash values.

• RandomPartitioner: uniformly distributes data across the cluster based on MD5 hash values.• ByteOrderedPartitioner: keeps an ordered distribution of data lexically by key bytes

The Murmur3Partitioner is the default partitioning strategy for new Cassandra clusters and the rightchoice for new clusters in almost all cases.

Set the partitioner in the cassandra.yaml file:

/documentation/cql/3.1/cql/cql_reference/create_keyspace_r.html


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• Murmur3Partitioner: org.apache.cassandra.dht.Murmur3Partitioner• RandomPartitioner: org.apache.cassandra.dht.RandomPartitioner• ByteOrderedPartitioner: org.apache.cassandra.dht.ByteOrderedPartitioner

Note: If using virtual nodes (vnodes), you do not need to calculate the tokens. If not using vnodes,you must calculate the tokens to assign to the initial_token parameter in the cassandra.yaml file.See Generating tokens and use the method for the type of partitioner you are using.

Murmur3PartitionerThe Murmur3Partitioner provides faster hashing and improved performance than the previous defaultpartitioner (RandomPartitioner).

You can only use Murmur3Partitioner for new clusters; you cannot change the partitioner in existingclusters. The Murmur3Partitioner uses the MurmurHash function. This hashing function creates a 64-bit hash value of the partition key. The possible range of hash values is from -263 to +263-1.

When using the Murmur3Partitioner, you can page through all rows using the token function in a CQLquery.

RandomPartitionerThe default partitioner prior to Cassandra 1.2.

The RandomPartitioner is included for backwards compatibility. You can use it in later versions ofCassandra, even when using virtual nodes (vnodes). However, if you don't use vnodes, you must calculatethe tokens, as described in Generating tokens.

The RandomPartition distributes data evenly across the nodes using an MD5 hash value of the rowkey. The possible range of hash values is from 0 to 2127 -1.

When using the RandomPartitioner, you can page through all rows using the token function in a CQLquery.

ByteOrderedPartitioner

The ByteOrderedPartitioner is included for backwards compatibility. Cassandra provides thispartitioner for ordered partitioning. This partitioner orders rows lexically by key bytes. You calculate tokensby looking at the actual values of your partition key data and using a hexadecimal representation of theleading character(s) in a key. For example, if you wanted to partition rows alphabetically, you could assignan A token using its hexadecimal representation of 41.

Using the ordered partitioner allows ordered scans by primary key. This means you can scan rows asthough you were moving a cursor through a traditional index. For example, if your application has usernames as the partition key, you can scan rows for users whose names fall between Jake and Joe. Thistype of query is not possible using randomly partitioned partition keys because the keys are stored in theorder of their MD5 hash (not sequentially).

Although having the capability to do range scans on rows sounds like a desirable feature of orderedpartitioners, there are ways to achieve the same functionality using table indexes.

Using an ordered partitioner is not recommended for the following reasons:

Difficult load balancing

More administrative overhead is required to load balance the cluster. An ordered partitioner requiresadministrators to manually calculate partition ranges based on their estimates of the partition key distribution.In practice, this requires actively moving node tokens around to accommodate the actual distribution of dataonce it is loaded.

Sequential writes can cause hot spots

/documentation/cql/3.1/cql/cql_using/paging_c.html

/documentation/cql/3.1/cql/cql_using/paging_c.html

/documentation/cql/3.1/cql/ddl/ddl_primary_index_c.html


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If your application tends to write or update a sequential block of rows at a time, then the writes are not bedistributed across the cluster; they all go to one node. This is frequently a problem for applications dealingwith timestamped data.

Uneven load balancing for multiple tables

If your application has multiple tables, chances are that those tables have different row keys and differentdistributions of data. An ordered partitioner that is balanced for one table may cause hot spots and unevendistribution for another table in the same cluster.

SnitchesA snitch determines which data centers and racks nodes belong to.

Snitches inform Cassandra about the network topology so that requests are routed efficiently and allowsCassandra to distribute replicas by grouping machines into data centers and racks. Specifically, thereplication strategy places the replicas based on the information provided by the new snitch. All nodesmust return to the same rack and data center. Cassandra does its best not to have more than one replicaon the same rack (which is not necessarily a physical location).

Note: If you change snitches, you may need to perform additional steps because the snitch affectswhere replicas are placed. See Switching snitches.

Dynamic snitchingMonitors the performance of reads from the various replicas and chooses the best replica based on thishistory.

By default, all snitches also use a dynamic snitch layer that monitors read latency and, when possible,routes requests away from poorly-performing nodes. The dynamic snitch is enabled by default and isrecommended for use in most deployments. For information on how this works, see Dynamic snitchingin Cassandra: past, present, and future. Configure dynamic snitch thresholds for each node in thecassandra.yaml configuration file.

For more information, see the properties listed under Failure detection and recovery.

SimpleSnitchFor single-data center deployments only.

The SimpleSnitch (the default) does not recognize data center or rack information. Use it for single-datacenter deployments or single-zone in public clouds. It treats strategy order as proximity, which can improvecache locality when disabling read repair.

Using a SimpleSnitch, you define the keyspace to use SimpleStrategy and specify a replication factor.

RackInferringSnitchDetermines the location of nodes by rack and data center corresponding to the IP addresses.

The RackInferringSnitch determines the proximaty of nodes by rack and data center, which are assumed tocorrespond to the 3rd and 2nd octet of the node's IP address, respectively. This snitch is best used as anexample for writing a custom snitch class (unless this happens to match your deployment conventions).

http://www.datastax.com/dev/blog/dynamic-snitching-in-cassandra-past-present-and-future


/documentation/cql/3.1/cql/cql_reference/cql_storage_options_c.html


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PropertyFileSnitchDetermines the location of nodes by rack and data center.

About this task

This snitch determines proximity is determined by rack and data center. It uses the network details locatedin the cassandra-topology.properties file. When using this snitch, you can define your data centernames to be whatever you want. Make sure that the data center names you define correlate to the nameof your data centers in your keyspace definition. Every node in the cluster should be described in thecassandra-topology.properties file, and this file should be exactly the same on every node in thecluster.

The location of the cassandra-topology.properties file depends on the type of installation:

• Package installations: /etc/cassandra/conf/cassandra-topology.properties• Tarball installations: install_location/conf/cassandra-topology.properties

Procedure

If you had non-uniform IPs and two physical data centers with two racks in each, and a third logical datacenter for replicating analytics data, the cassandra-topology.properties file might look like this:

# Data Center One

175.56.12.105 =DC1:RAC1175.50.13.200 =DC1:RAC1175.54.35.197 =DC1:RAC1


# Data Center Two



# Analytics Replication Group


# default for unknown nodes default =DC3:RAC1

GossipingPropertyFileSnitchAutomatically updates all nodes using gossip when adding new nodes.

This snitch is recommended for production. It uses rack and data center information for the local nodedefined in the cassandra-rackdc.properties file and propagates this information to other nodes viagossip.

The cassandra-rackdc.properties file defines the default data center and rack used by this snitch:

dc=DC1rack=RAC1

The location of the conf directory depends on the type of installation:



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• Package installations: /etc/cassandra/conf/cassandra-rackdc.properties• Tarball installations: install_location/conf/cassandra-rackdc.properties

To allow migration from the PropertyFileSnitch, it uses the cassandra-topology.properties file if itis present.

EC2SnitchUse with Amazon EC2 in a single region.

Use the EC2Snitch for simple cluster deployments on Amazon EC2 where all nodes in the cluster arewithin a single region.

The region name is treated as the data center name and availability zones are treated as racks within adata center. For example, if a node is in the us-east-1 region, us-east is the data center name and 1 isthe rack location. (Racks are important for distributing replicas, but not for data center naming.) Becauseprivate IPs are used, this snitch does not work across multiple regions.

If you are using only a single data center, you do not need to specify any properties.

If you need multiple data centers, set the dc_suffix options in the cassandra-rackdc.properties file.Any other lines are ignored. The location of this file depends on the type of installation:


For example, for each node within the us-east region, specify the data center in its cassandra-rackdc.properties file:

• node0

dc_suffix=_1_cassandra

• node1


• node2


• node3


• node4

dc_suffix=_1_analytics

• node5

dc_suffix=_1_search

This results in three data centers for the region:

us-east_1_cassandraus-east_1_analyticsus-east_1_search

Note: The data center naming convention in this example is based on the workload. You can useother conventions, such as DC1, DC2 or 100, 200.

Keyspace strategy options

When defining your keyspace strategy options, use the EC2 region name, such as ``us-east``, as your datacenter name.



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EC2MultiRegionSnitchUse with Amazon EC2 in multiple regions.

Use the EC2MultiRegionSnitch for deployments on Amazon EC2 where the cluster spans multiple regions.

The region name is treated as the data center name and availability zones are treated as racks within adata center. For example, if a node is in the us-east-1 region, us-east is the data center name and 1 is therack location. (Racks are important for distributing replicas, but not for data center naming.)

The dc_suffix options in the cassandra-rackdc.properties file defines the data centers used by thissnitch. Any other lines are ignored. The location of this file depends on the type of installation:


For example, for two regions with the data centers named for their workloads and two cassandra datacenters:

For each node in the us-east region, specify its data center in cassandra-rackdc.properties file:

• node0


• node1


• node2


• node3


• node4


• node5

dc_suffix=_1_search

This results in four us-east data centers:

us-east_1_cassandraus-east_2_cassandraus-east_1_analyticsus-east_1_search

For each node in the us-west region, specify its data center in cassandra-rackdc.properties file:

• node0


• node1


• node2


• node3


• node4


• node5

dc_suffix=_1_search


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This results in four us-west data centers:

us-west_1_cassandraus-west_2_cassandraus-west_1_analyticsus-west_1_search

Note: The data center naming convention in this example is based on the workload. You can useother conventions, such as DC1, DC2 or 100, 200.

Other configuration settings

This snitch uses public IP as broadcast_address to allow cross-region connectivity. This means you mustconfigure each node for cross-region communication:

1. Set the listen_address to the private IP address of the node, and the broadcast_address is set to thepublic IP address of the node.

This allows Cassandra nodes in one EC2 region to bind to nodes in another region, thus enablingmultiple data center support. (For intra-region traffic, Cassandra switches to the private IP afterestablishing a connection.)

2. Set the addresses of the seed nodes in the cassandra.yaml file to that of the public IP (private IP arenot routable between networks). For example:

seeds: 50.34.16.33, 60.247.70.52

To find the public IP address, from each of the seed nodes in EC2:

$ curl http://instance-data/latest/meta-data/public-ipv4

Note: Do not make all nodes seeds, see Internode communications (gossip).

3. Be sure that the storage_port or ssl_storage_port is open on the public IP firewall.

Keyspace strategy options

When defining your keyspace strategy options, use the EC2 region name, such as ``us-east``, as your datacenter name.

GoogleCloudSnitch

Use the GoogleCloudSnitch for Cassandra deployments on Google Cloud Platform across one or moreregions. The region is treated as a data center and the availability zones are treated as racks within thedata center. All communication occurs over private IP addresses within the same logical network.

CloudstackSnitch

Use the CloudstackSnitch for Apache Cloudstack environments. Because zone naming is free-form inApache Cloudstack, this snitch uses the widely-used <country> <location> <az> notation.

Client requestsClient read or write requests can be sent to any node in the cluster because all nodes in Cassandra arepeers.

When a client connects to a node and issues a read or write request, that node serves as the coordinatorfor that particular client operation.

The job of the coordinator is to act as a proxy between the client application and the nodes (or replicas)that own the data being requested. The coordinator determines which nodes in the ring should get therequest based on the cluster configured partitioner and replica placement strategy.


https://cloud.google.com/

http://cloudstack.apache.org/

Planning a cluster deployment

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When planning a Cassandra cluster deployment, you should have a good idea of the initial volume of datayou plan to store and a good estimate of your typical application workload.

The following topics provide information for planning your cluster:

Selecting hardware for enterprise implementationsChoosing appropriate hardware depends on selecting the right balance of the following resources:memory, CPU, disks, number of nodes, and network.

Memory

The more memory a Cassandra node has, the better read performance. More RAM also allows memorytables (memtables) to hold more recently written data. Larger memtables lead to a fewer number ofSSTables being flushed to disk and fewer files to scan during a read. The ideal amount of RAM dependson the anticipated size of your hot data.

• For dedicated hardware, the optimal price-performance sweet spot is 16GB to 64GB; the minimum is8GB.

• For a virtual environments, the optimal range may be 8GB to 16GB; the minimum is 4GB.• For setting Java heap space, see Tuning Java resources.

CPU

Insert-heavy workloads are CPU-bound in Cassandra before becoming memory-bound. (All writes go tothe commit log, but Cassandra is so efficient in writing that the CPU is the limiting factor.) Cassandra ishighly concurrent and uses as many CPU cores as available:

• For dedicated hardware, 8-core CPU processors are the current price-performance sweet spot.• For virtual environments, consider using a provider that allows CPU bursting, such as Rackspace Cloud

Servers.

Disk

Disk space depends on usage, so it's important to understand the mechanism. Cassandra writes datato disk when appending data to the commit log for durability and when flushing memtable to SSTabledata files for persistent storage. The commit log has a different access pattern (read/writes ratio) than thepattern for accessing data from SSTables. This is more important for spinning disks than for SSDs (solidstate drives). See the recommendations below.

SSTables are periodically compacted. Compaction improves performance by merging and rewritingdata and discarding old data. However, depending on the type of compaction strategy and size ofthe compactions, during compaction disk utilization and data directory volume temporarily increases.For this reason, you should leave an adequate amount of free disk space available on a node.For large compactions, leave an adequate amount of free disk space available on a node: 50%(worst case) for SizeTieredCompactionStrategy and DateTieredCompactionStrategy, and 10% forLeveledCompactionStrategy. For more information about compaction, see:

• Compaction• The Apache Cassandra storage engine• Leveled Compaction in Apache Cassandra• When to Use Leveled Compaction

For information on calculating disk size, see Calculating usable disk capacity.


http://2012.nosql-matters.org/cgn/wp-content/uploads/2012/06/Sylvain_Lebresne-Cassandra_Storage_Engine.pdf

http://www.datastax.com/dev/blog/leveled-compaction-in-apache-cassandra

http://www.datastax.com/dev/blog/when-to-use-leveled-compaction


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Recommendations:

Capacity per node

Most workloads work best with a capacity under 500GB to 1TB per node depending on I/O. Maximumrecommended capacity for Cassandra 1.2 and later is 3 to 5TB per node for uncompressed data. ForCassandra 1.1, it is 500 to 800GB per node. Be sure to account for replication.

Capacity and I/O

When choosing disks, consider both capacity (how much data you plan to store) and I/O (the write/readthroughput rate). Some workloads are best served by using less expensive SATA disks and scaling diskcapacity and I/O by adding more nodes (with more RAM).

Solid-state drives

SSDs are recommended for Cassandra. The NAND Flash chips that power SSDs provide extremelylow-latency response times for random reads while supplying ample sequential write performance forcompaction operations. A large variety of SSDs are available on the market from server vendors and third-party drive manufacturers. DataStax customers that need help in determining the most cost-effective optionfor a given deployment and workload, should contact their Solutions Engineer or Architect. Unlike spinningdisks, it's all right to store both commit logs and SSTables are on the same mount point.

Number of disks - SATA

Ideally Cassandra needs at least two disks, one for the commit log and the other for the data directories.At a minimum the commit log should be on its own partition.

Commit log disk - SATA

The disk need not be large, but it should be fast enough to receive all of your writes as appends (sequentialI/O).

Data disks

Use one or more disks and make sure they are large enough for the data volume and fast enough to bothsatisfy reads that are not cached in memory and to keep up with compaction.

RAID on data disks

It is generally not necessary to use RAID for the following reasons:

• Data is replicated across the cluster based on the replication factor you've chosen.• Starting in version 1.2, Cassandra includes a JBOD (Just a bunch of disks) feature to take care of disk

management. Because Cassandra properly reacts to a disk failure either by stopping the affected nodeor by blacklisting the failed drive, you can deploy Cassandra nodes with large disk arrays without theoverhead of RAID 10. You can configure Cassandra to stop the affected node or blacklist the driveaccording to your availability/consistency requirements.

RAID on the commit log disk

Generally RAID is not needed for the commit log disk. Replication adequately prevents data loss. If youneed extra redundancy, use RAID 1.

Extended file systems

DataStax recommends deploying Cassandra on XFS or ext4. On ext2 or ext3, the maximum file size is 2TBeven using a 64-bit kernel. On ext4 it is 16TB.

Because Cassandra can use almost half your disk space for a single file when usingSizeTieredCompactionStrategy, use XFS when using large disks, particularly if using a 32-bit kernel. XFSfile size limits are 16TB max on a 32-bit kernel, and essentially unlimited on 64-bit.

Number of nodes

Prior to version 1.2, the recommended size of disk space per node was 300 to 500GB. Improvement toCassandra 1.2, such as JBOD support, virtual nodes (vnodes), off-heap Bloom filters, and parallel leveledcompaction (SSD nodes only), allow you to use few machines with multiple terabytes of disk space.


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Network

Since Cassandra is a distributed data store, it puts load on the network to handle read/write requests andreplication of data across nodes. Be sure that your network can handle traffic between nodes withoutbottlenecks. You should bind your interfaces to separate Network Interface Cards (NIC). You can usepublic or private depending on your requirements.

• Recommended bandwidth is 1000 Mbit/s (gigabit) or greater.• Thrift/native protocols use the rpc_address.• Cassandra's internal storage protocol uses the listen_address.

Cassandra efficiently routes requests to replicas that are geographically closest to the coordinator nodeand chooses a replica in the same rack if possible; it always chooses replicas located in the same datacenter over replicas in a remote data center.

Firewall

If using a firewall, make sure that nodes within a cluster can reach each other. See Configuring firewall portaccess.

Planning an Amazon EC2 cluster

Before planning an Amazon EC2 cluster, please see the User guide in the Amazon Elastic Compute CloudDocumentation.

DataStax AMI deployments

The DataStax AMI is intended only for a single region and availability zone. For an EC2 cluster that spansmultiple regions and availability zones, see EC2 clusters spanning multiple regions and availability zones.

Use AMIs from trusted sources

Use only AMIs from a trusted source. Random AMI's pose a security risk and may perform slower thanexpected due to the way the EC2 install is configured. The following are examples of trusted AMIs:

• Ubuntu Amazon EC2 AMI Locator• Debian AmazonEC2Image• CentOS-6 images on Amazon's EC2 Cloud

EC2 clusters spanning multiple regions and availability zones

When creating an EC2 cluster that spans multiple regions and availability zones, use OpsCenter to set upyour cluster. You can use any of the supported platforms. It is best practice to use the same platform onall nodes. If your cluster was instantiated using the DataStax AMI, use Ubuntu for the additional nodes.Configure the cluster as a multiple data center cluster using the EC2MultiRegionSnitch. The followingtopics describe OpsCenter provisioning:

• Provisioning a new cluster• Adding an existing cluster• Adding nodes to a cluster

Production Cassandra clusters on EC2

For production Cassandra clusters on EC2, use these guidelines for choosing the instance types:

• Development and light production: m3.large• Moderate production: m3.xlarge• SSD production with light data: c3.2xlarge

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/concepts.html

http://cloud-images.ubuntu.com/locator/ec2/

https://wiki.debian.org/Cloud/AmazonEC2Image

http://wiki.centos.org/Cloud/AWS

http://planetcassandra.org/cassandra/

/documentation/opscenter/5.0/opsc/online_help/opscCreatingCluster_t.html

/documentation/opscenter/5.0/opsc/online_help/opscAddingCluster_t.html

/documentation/opscenter/5.0/opsc/online_help/opscAddingNode_t.html


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• Largest heavy production: m3.2xlarge (PV) or i2.2xlarge (HVM)

Note: The main difference between m1 and m3 instance types for use with Cassandra is thatm3 instance types have faster, smaller SSD drives and m1 instance types have slower, largerrotational drives. Use m1 instance types when you have higher tolerance for latency SLAs and yourequire smaller cluster sizes, or both. For more aggressive workloads use m3 instance types withappropriately sized clusters.

EBS volumes are not recommended

EBS volumes are not recommended for Cassandra data storage volumes for the following reasons:

• EBS volumes contend directly for network throughput with standard packets. This contention meansthat EBS throughput is likely to fail if you saturate a network link.

• EBS volumes have unreliable performance. I/O performance can be exceptionally slow, causing thesystem to back load reads and writes until the entire cluster becomes unresponsive.

• Adding capacity by increasing the number of EBS volumes per host does not scale. You can easilysurpass the ability of the system to keep effective buffer caches and concurrently serve requests for allof the data it is responsible for managing.

Note: Use only ephemeral instance-store devices for Cassandra data storage.

For more information and graphs related to ephemeral versus EBS performance, see the blog articleSystematic Look at EC2 I/O.

Disk Performance Optimization

To ensure high disk performance to mounted drives, it is recommended that you pre-warm your drivesby writing once to every drive location before production use. Depending on EC2 conditions, you can getmoderate to enormance increases in throughput. See Optimizing Disk Performance in the Amazon ElasticCompute Cloud Documentation.

Storage recommendations for Cassandra 1.2 and later

Cassandra 1.2 and later supports JBOD (just a bunch of disks). JBOD excels at tolerating partial failures ina disk array. Configure using the disk_failure_policy in the cassandra.yaml file. Addition information isavailable in the Handling Disk Failures In Cassandra 1.2 blog.

Note: Cassandra JBOD support allows you to use standard disks. However, RAID0 may providebetter throughput because it splits every block to be on another device. This means that writes arewritten in parallel fashion instead of written serially on disk.

Storage recommendations for Cassandra 1.1 and earlier

RAID 0 the ephemeral disks. Then put both the data directory and the commit log on that volume.This has proved to be better in practice than putting the commit log on the root volume, which is also ashared resource. For more data redundancy, consider deploying your Cassandra cluster across multipleavailability zones or using EBS volumes to store your Cassandra backup files.

Calculating usable disk capacityDetermining how much data your Cassandra nodes can hold.

About this task

To calculate how much data your Cassandra nodes can hold, calculate the usable disk capacity per nodeand then multiply that by the number of nodes in your cluster. Remember that in a production cluster, youwill typically have your commit log and data directories on different disks.

http://blog.scalyr.com/2012/10/16/a-systematic-look-at-ec2-io/

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/InstanceStorage.html#disk-performance

http://www.datastax.com/dev/blog/handling-disk-failures-in-cassandra-1-2


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Procedure

1. Start with the raw capacity of the physical disks:

raw_capacity = disk_size * number_of_data_disks

2. Calculate the formatted disk space as follows:

formatted_disk_space = (raw_capacity * 0.9)

During normal operations, Cassandra routinely requires disk capacity for compaction and repairoperations. For optimal performance and cluster health, DataStax recommends not filling your disksto capacity, but running at 50% to 80% capacity depending on the compaction strategy and size of thecompactions.

3. Calculate the usuable disk space accounting for file system formatting overhead (roughly 10 percent):

usable_disk_space = formatted_disk_space * (0.5 to 0.8)

Calculating user data sizeAccounting for storage overhead in determining user data size.

About this task

The size of your raw data may be larger or smaller once it is loaded into Cassandra due to storageoverhead. How much depends on how well it compresses and the characteristics of your data and tables.The following calculations account for data persisted to disk, not for data stored in memory.

Procedure

• Determine column overhead:

regular_total_column_size = column_name_size + column_value_size + 15

counter - expiring_total_column_size = column_name_size + column_value_size + 23

Every column in Cassandra incurs 15 bytes of overhead. Since each row in a table can have differentcolumn names as well as differing numbers of columns, metadata is stored for each column. Forcounter columns and expiring columns, you should add an additional 8 bytes (23 bytes total).

• Account for row overhead.

Every row in Cassandra incurs 23 bytes of overhead.• Estimate primary key index size:

primary_key_index = number_of_rows * ( 32 + average_key_size )

Every table also maintains a partition index. This estimation is in bytes.• Determine replication overhead:

replication_overhead = total_data_size * ( replication_factor - 1 )

The replication factor plays a role in how much disk capacity is used. For a replication factor of 1, thereis no overhead for replicas (as only one copy of data is stored in the cluster). If replication factor isgreater than 1, then your total data storage requirement will include replication overhead.



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Anti-patterns in CassandraImplementation or design patterns that are ineffective and/or counterproductive in Cassandra productioninstallations. Correct patterns are suggested in most cases.

Network attached storage

Storing SSTables on a network attached storage (NAS) device is not recommended. Using a NAS deviceoften results in network related bottlenecks resulting from high levels of I/O wait time on both reads andwrites. The causes of these bottlenecks include:

• Router latency.• The Network Interface Card (NIC) in the node.• The NIC in the NAS device.

If you are required to use NAS for your environment, please contact a technical resource from DataStax forassistance.

Shared network file systems

Shared network file systems (NFS) have the same limitations as NAS. The temptation with NFSimplementations is to place all SSTables in a node into one NFS. Doing this deprecates one ofCassandra's strongest features: No Single Point of Failure (SPOF). When all SSTables from all nodes arestored onto a single NFS, the NFS becomes a SPOF. To best use Cassandra, avoid using NFS.

Excessive heap space size

DataStax recommends using the default heap space size for most use cases. Exceeding this size canimpair the Java virtual machine's (JVM) ability to perform fluid garbage collections (GC). The followingtable shows a comparison of heap space performances reported by a Cassandra user:

Heap CPU utilization Queries per second Latency

40 GB 50% 750 1 second

8 GB 5% 8500 (not maxed out) 10 ms

For information on heap sizing, see Tuning Java resources.

Cassandra's rack feature

Defining one rack for the entire cluster is the simplest and most common implementation. Multiple racksshould be avoided for the following reasons:

• Most users tend to ignore or forget rack requirements that racks should be organized in an alternatingorder. This order allows the data to get distributed safely and appropriately.

• Many users are not using the rack information effectively. For example, setting up with as many racksas nodes (or similar non-beneficial scenarios).

• Expanding a cluster when using racks can be tedious. The procedure typically involves several nodemoves and must ensure that racks are distributing data correctly and evenly. When clusters needimmediate expansion, racks should be the last concern.

To use racks correctly:

• Use the same number of nodes in each rack.• Use one rack and place the nodes in different racks in an alternating pattern. This allows you to still get

the benefits of Cassandra's rack feature, and allows for quick and fully functional expansions. Once thecluster is stable, you can swap nodes and make the appropriate moves to ensure that nodes are placedin the ring in an alternating fashion with respect to the racks.


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SELECT ... IN or index lookups

SELECT ... IN and index lookups (formerly secondary indexes) should be avoided except for specificscenarios. See When not to use IN in SELECT and When not to use an index in Indexing in CQL forCassandra 2.0.

Using the Byte Ordered Partitioner

The Byte Ordered Partitioner (BOP) is not recommended.

Use virtual nodes (vnodes) and use either the Murmur3Partitioner (default) or the RandomPartitioner.Vnodes allow each node to own a large number of small ranges distributed throughout the cluster. Usingvnodes saves you the effort of generating tokens and assigning tokens to your nodes. If not using vnodes,these partitioners are recommended because all writes occur on the hash of the key and are thereforespread out throughout the ring amongst tokens range. These partitioners ensure that your cluster evenlydistributes data by placing the key at the correct token using the key's hash value.

Reading before writingReads take time for every request, as they typically have multiple disk hits for uncached reads. In workflows requiring reads before writes, this small amount of latency can affect overall throughput. All write I/O in Cassandra is sequential so there is very little performance difference regardless of data size or keydistribution.

Load balancers

Cassandra was designed to avoid the need for load balancers. Putting load balancers between Cassandraand Cassandra clients is harmful to performance, cost, availability, debugging, testing, and scaling. Allhigh-level clients, such as the Java and Python drivers for Cassandra, implement load balancing directly.

Insufficient testing

Be sure to test at scale and production loads. This the best way to ensure your system will functionproperly when your application goes live. The information you gather from testing is the best indicator ofwhat throughput per node is needed for future expansion calculations.

To properly test, set up a small cluster with production loads. There will be a maximum throughputassociated with each node count before the cluster can no longer increase performance. Take themaximum throughput at this cluster size and apply it linearly to a cluster size of a different size. Nextextrapolate (graph) your results to predict the correct cluster sizes for required throughputs for yourproduction cluster. This allows you to predict the correct cluster sizes for required throughputs in the future.The Netflix case study shows an excellent example for testing.

Lack of familiarity with Linux

Linux has a great collection of tools. Become familiar with the Linux built-in tools. It will help you greatlyand ease operation and management costs in normal, routine functions. The essential list of tools andtechniques to learn are:

• Parallel SSH and Cluster SSH: The pssh and cssh tools allow SSH access to multiple nodes. This isuseful for inspections and cluster wide changes.

• Passwordless SSH: SSH authentication is carried out by using public and private keys. This allows SSHconnections to easily hop from node to node without password access. In cases where more security isrequired, you can implement a bastion host and/or VPN.

• Useful common command-line tools include:

• dstat: Shows all system resources instantly. For example, you can compare disk usage incombination with interrupts from your IDE controller, or compare the network bandwidth numbersdirectly with the disk throughput (in the same interval).

• top: Provides an ongoing look at CPU processor activity in real time.

/documentation/cql/3.1/cql/cql_reference/select_r.html


/documentation/developer/java-driver/2.0/java-driver/whatsNew2.html

/documentation/developer/python-driver/2.0/common/drivers/introduction/introArchOverview_c.html

http://www.datastax.com/1-million-writes


31

• System performance tools: Tools such as iostat, mpstat, iftop, sar, lsof, netstat, htop, vmstat, andsimilar can collect and report a variety of metrics about the operation of the system.

• vmstat: Reports information about processes, memory, paging, block I/O, traps, and CPU activity.• iftop: Shows a list of network connections. Connections are ordered by bandwidth usage, with the

pair of hosts responsible for the most traffic at the top of list. This tool makes it easier to identify thehosts causing network congestion.

Running without the recommended settings

Be sure to use the recommended settings in the Cassandra documentation.

Also be sure to consult the Planning a Cassandra cluster deployment documentation, which discusseshardware and other recommendations before making your final hardware purchases.

More anti-patternsFor more about anti-patterns, visit Matt Dennis` slideshare.

http://www.slideshare.net/mattdennis

Installing DataStax Community

32


Installing DataStax Community on RHEL-based systemsInstall using Yum repositories on RHEL, CentOS, and Oracle Linux.

Note: To install on SUSE, use the Cassandra binary tarball distribution.

For a complete list of supported platforms, see DataStax Community – Supported Platforms.

Before you begin

• Yum Package Management application installed.• Root or sudo access to the install machine.• Latest version of Oracle Java SE Runtime Environment (JRE) 7. See Installing the JRE on RHEL-based

systems.• Python 2.6+ (needed if installing OpsCenter).

About this task

The packaged releases create a cassandra user. When starting Cassandra as a service, the service runsas this user. The following utilities are included in a separate package: sstable2json, sstablelevelreset,sstablemetadata, json2sstable, sstablerepairedset, sstablesplit, and token-generator.

Procedure

In a terminal window:

1. Check which version of Java is installed by running the following command:

$ java -version

Use the latest version of Oracle Java 7 on all nodes.

2. Add the DataStax Community repository to the /etc/yum.repos.d/datastax.repo:

[datastax] name = DataStax Repo for Apache Cassandrabaseurl = http://rpm.datastax.com/communityenabled = 1gpgcheck = 0

3. Install the packages:

$ sudo yum install dsc21$ sudo yum install cassandra21-tools ## Installs optional utilities.

The DataStax Community distribution of Cassandra is ready for configuration.

What to do next

• Initializing a multiple node cluster (single data center)• Initializing a multiple node cluster (multiple data centers)• Recommended production settings• Installing OpsCenter• Key components for configuring Cassandra• Starting Cassandra as a service

http://planetcassandra.org/Download/DataStaxCommunityEdition

/documentation/opscenter/4.0/opsc/install/opscInstallOpsc_g.html


33

• Package installation directories

Installing DataStax Community on Debian-based systemsInstall using APT repositories on Debian and Ubuntu.


Before you begin

• Advanced Package Tool is installed.• Root or sudo access to the install machine.• Python 2.6+ (needed if installing OpsCenter).• Latest version of Oracle Java SE Runtime Environment (JRE) 7. See Installing the JRE on Debian-

based systems.

About this task

The packaged releases create a cassandra user. When starting Cassandra as a service, the service runsas this user. The following utilities are included in a separate package: sstable2json, sstablelevelreset,sstablemetadata, json2sstable, sstablerepairedset, sstablesplit, and token-generator.

Procedure



$ java -version


2. Add the DataStax Community repository to the /etc/apt/sources.list.d/cassandra.sources.list

$ echo "deb http://debian.datastax.com/community stable main" | sudo tee -a /etc/apt/sources.list.d/cassandra.sources.list

3. Debian systems only:

a) In /etc/apt/sources.list, find the line that describes your source repository for Debian andadd contrib non-free to the end of the line. For example:

deb http://some.debian.mirror/debian/ $distro main contrib non-free

This allows installation of the Oracle JVM instead of the OpenJDK JVM.b) Save and close the file when you are done adding/editing your sources.

4. Add the DataStax repository key to your aptitude trusted keys.

$ curl -L http://debian.datastax.com/debian/repo_key | sudo apt-key add -

5. Install the latest package:

$ sudo apt-get update$ sudo apt-get install dsc21$ sudo apt-get install cassandra-tools ## Optional utilities

Note: To install an earlier version of DataStax Community:

$ sudo apt-get install dsc21=2.1.x-1 cassandra=2.1.x$ sudo apt-get install dsc21=2.1.x-1 cassandra=2.1.1 cassandra-tools=2.1.x ## Optional



34

This installs the DataStax Community distribution of Cassandra. .

6. Because the Debian packages start the Cassandra service automatically, you must stop the server andclear the data:

Doing this removes the default cluster_name (Test Cluster) from the system table. All nodes must usethe same cluster name.

$ sudo service cassandra stop$ sudo rm -rf /var/lib/cassandra/data/system/*


What to do next

• Initializing a multiple node cluster (single data center)• Initializing a multiple node cluster (multiple data centers)• Recommended production settings• Installing OpsCenter• Key components for configuring Cassandra• Starting Cassandra as a service• Package installation directories

Installing DataStax Community on any Linux-based platformInstall on all Linux-based platforms using a binary tarball.

About this taskUse this install for Mac OS X and platforms without package support, or if you do not have or want a rootinstallation.


Before you begin

• Latest version of Oracle Java SE Runtime Environment (JRE) 7. See Installing the JRE.• Python 2.6+ (needed if installing OpsCenter).• If you are using an older RHEL-based Linux distribution, such as CentOS-5, you may see the following

error: GLIBCXX_3.4.9 not found. You must replace the Snappy compression/decompressionlibrary (snappy-java-1.0.5.jar) with the snappy-java-1.0.4.1.jar.

About this task

The binary tarball runs as a stand-alone process.

Procedure



$ java -version


2. Download the DataStax Community:

$ curl -L http://downloads.datastax.com/community/dsc.tar.gz | tar xz



https://snappy-java.googlecode.com/files/snappy-java-1.0.4.1.jar


35

You can also download from Planet Cassandra.

3. Go to the install directory:

$ cd dsc-cassandra-2.1.x


4. Go to the install directory:

$ cd install_location/apache-cassandra-2.1.x

Cassandra is ready for configuration.

What to do next

• Initializing a multiple node cluster (single data center)• Initializing a multiple node cluster (multiple data centers)• Recommended production settings• Installing OpsCenter• Key components for configuring Cassandra• Tarball installation directories• Starting Cassandra as a stand-alone process

Installing DataStax Community on Windows systems

About this task

To install on Windows systems, see the Getting started guide.

Installing on cloud providers

Installing a Cassandra cluster on Amazon EC2A step-by-step guide for installing the DataStax Community AMI (Amazon Machine Image).

About this task

The DataStax AMI allows you to set up a simple DataStax Community cluster using the Amazon WebServices EC2 Management Console. Installing via the AMI allows you to quickly deploy a Cassandracluster within a single availability zone.

The AMI does the following:

• Installs the latest version of Cassandra with an Ubuntu 12.04 LTS (Precise Pangolin), image (UbuntuCloud 20140227 release), Kernel 3.8+.

• Installs Oracle Java 7.• Install metrics tools such as dstat, ethtool, make, gcc, and s3cmd.• Uses RAID0 ephemeral disks for data storage and commit logs.• Choice of PV (Para-virtualization) or HVM (Hardware-assisted Virtual Machine) instance types. See

Amazon documentation.• Launches EBS-backed instances for faster start-up, not database storage.• Uses the private interface for intra-cluster communication.• Sets the seed nodes cluster-wide.• Installs OpsCenter (by default).

http://planetcassandra.org/


/documentation/getting_started/doc/getting_started/gettingStartedWindows_t.html

http://aws.amazon.com/ec2/

http://aws.amazon.com/ec2/

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/virtualization_types.html


36

Note: When creating an EC2 cluster that spans multiple regions and availability zones, useOpsCenter to set up your cluster. See EC2 clusters spanning multiple regions and availabilityzones.

Because Amazon changes the EC2 console intermittently, these instructions have been generalized. Fordetails on each step, see the User guide in the Amazon Elastic Compute Cloud Documentation.

To install a Cassandra cluster from the DataStax AMI, complete the following tasks:

Creating an EC2 security group

About this task

An EC2 Security Group acts as a firewall that allows you to choose which protocols and ports are open inyour cluster. You must specify a security group in the same region as your instances.

You can specify the protocols and ports either by a range of IP addresses or by security group. To protectyour cluster, you should define a security group. Be aware that specifying a Source IP of 0.0.0.0/0 allowsevery IP address access by the specified protocol and port range.

Procedure

If you need more help, click an informational icon or a link to the Amazon EC2 User Guide.

1. Sign in to the AWS console.

2. From the Amazon EC2 console navigation bar, select the same region as where you will launch theDataStax Community AMI.

Step 1 in Launch instances provides a list of the available regions.

3. Open the Security Groups page.

4. Create a security group with a name and description of your choice, then save it. It is recommendedthat you include the region name in the description.

Note: Creating and saving the securing group allows you to create rules based on the group.After the security group is saved it is available in the Source field drop-list.

5. Create rules for the security group using the following table:

Table 1: Ports

Portnumber

Type Protocol Source Description

Public ports

22 SSH TCP 0.0.0.0/0 SSH port

8888 CustomTCPRule

TCP 0.0.0.0/0 OpsCenter website. The opscenterd daemon listenson this port for HTTP requests coming directly fromthe browser.


http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EC2_Network_and_Security.html

http://aws.amazon.com/console/


37

Portnumber

Type Protocol Source Description

Cassandra inter-node ports

1024 -65355

CustomTCPRule

TCP Yoursecuritygroup

Cassandra 1.2 or earlier only. Because JMXconnects on port 7199, handshakes, and thenuses any port within the 1024+ range, use SSH toexecute commands remotely to connect to JMXlocally or use the DataStax OpsCenter.

7000 CustomTCPRule


Cassandra inter-node cluster communication.

7001 CustomTCPRule


Cassandra SSL inter-node cluster communication.

7199 CustomTCPRule


Cassandra JMX monitoring port.

Cassandra client ports

9042 CustomTCPRule

TCP 0.0.0.0/0 Cassandra client port.

9160 CustomTCPRule

TCP 0.0.0.0/0 Cassandra client port (Thrift).

OpsCenter inter-node ports

61620 CustomTCPRule


OpsCenter monitoring port. The opscenterd daemonlistens on this port for TCP traffic coming from theagent.

61621 CustomTCPRule


OpsCenter agent port. The agents listen on this portfor SSL traffic initiated by OpsCenter.

The completed port rules should look similar to this:

Warning: The security configuration shown in this example opens up all externally accessibleports to incoming traffic from any IP address (0.0.0.0/0). The risk of data loss is high. If youdesire a more secure configuration, see the Amazon EC2 help on security groups.


38

Creating a key pair

About this task

Amazon EC2 uses public–key cryptography to encrypt and decrypt login information. Public–keycryptography uses a public key to encrypt data and the recipient uses the private key to decrypt the data.The public and private keys are known as a key pair.

Procedure

You must create a key pair for each region you use.

1. From the Amazon EC2 console navigation bar, select the same region as where you will launch theDataStax Community AMI.

Step 1 in Launch instances provides a list of the available regions.

2. Create the key pair and save it to your home directory.

3. Set the permissions of your private key file so that only you can read it.

$ chmod 400 my-key-pair.pem

Launching the DataStax Community AMI

About this task

After creating the security group, you can launch your AMI instances.

Procedure

If you need more help, click an informational icon or a link to the Amazon EC2 User Guide.

1. Launch the AMI using the links in the following table:

Amazon EC2 offers a number of geographic regions for launching the AMI. Factors for choosing aregion include: reduce latency, cost, or regulatory requirements.

Region AMI

HVM instances (Hardware-assisted Virtual Machine - see Amazon documentation.)

us-east-1 ami-ada2b6c4

us-west-1 ami-3cf7c979

us-west-2 ami-1cff962c

eu-west-1 ami-7f33cd08

ap-southeast-1 ami-b47828e6

ap-southeast-2 ami-55d54d6f

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-regions-availability-zones.html


https://console.aws.amazon.com/ec2/home?region=us-east-1#launchAmi=ami-ada2b6c4

https://console.aws.amazon.com/ec2/home?region=us-west-1#launchAmi=ami-3cf7c979

https://console.aws.amazon.com/ec2/home?region=us-west-2#launchAmi=ami-1cff962c

https://console.aws.amazon.com/ec2/home?region=eu-west-1#launchAmi=ami-7f33cd08

https://console.aws.amazon.com/ec2/home?region=ap-southeast-1#launchAmi=ami-b47828e6

https://console.aws.amazon.com/ec2/home?region=ap-southeast-2#launchAmi=ami-55d54d6f


39

Region AMI

ap-northeast-1 ami-714a3770

sa-east-1 ami-1dda7800

PV instances (Paravirtualization - see Amazon documentation.

us-east-1 ami-f9a2b690

us-west-1 ami-32f7c977

us-west-2 ami-16ff9626

eu-west-1 ami-8932ccfe

ap-southeast-1 ami-8c7828de

ap-southeast-2 ami-57d54d6d

ap-northeast-1 ami-6b4a376a

sa-east-1 ami-15da7808

2. In Step 2: Choose an Instance Type, choose the appropriate type.

The recommended instances are:

• Development and light production: m3.large• Moderate production: m3.xlarge• SSD production with light data: c3.2xlarge• Largest heavy production: m3.2xlarge (PV) or i2.2xlarge (HVM)• Micro, small, and medium types are not supported.

Note: The main difference between m1 and m3 instance types for use with Cassandra is thatm3 instance types have faster, smaller SSD drives and m1 instance types have slower, largerrotational drives. Use m1 instance types when you have higher tolerance for latency SLAs andyou require smaller cluster sizes, or both. For more aggressive workloads use m3 instance typeswith appropriately sized clusters.

When the instance is selected, its specifications are displayed:

Because Amazon updates instance types periodically, see the following docs to help you determineyour hardware and storage requirements:

• Planning a cluster deployment• User guide in the Amazon Elastic Compute Cloud Documentation• What is the story with AWS storage• Get in the Ring with Cassandra and EC2

3. Click Next: Configure Instance Details and configure the instances to suit your requirements:

• Number of instances• Network - Select Launch into EC2-Classic.• Advanced Details - Open and add the following options (as text) to the User Data section.

Option Description

--clusternamename

Required. The name of the cluster.

https://console.aws.amazon.com/ec2/home?region=ap-northeast-1#launchAmi=ami-714a3770

https://console.aws.amazon.com/ec2/home?region=sa-east-1#launchAmi=ami-1dda7800


https://console.aws.amazon.com/ec2/home?region=us-east-1#launchAmi=ami-f9a2b690

https://console.aws.amazon.com/ec2/home?region=us-west-1#launchAmi=ami-32f7c977

https://console.aws.amazon.com/ec2/home?region=us-west-2#launchAmi=ami-16ff9626

https://console.aws.amazon.com/ec2/home?region=eu-west-1#launchAmi=ami-8932ccfe

https://console.aws.amazon.com/ec2/home?region=ap-southeast-1#launchAmi=ami-8c7828de

https://console.aws.amazon.com/ec2/home?region=ap-southeast-2#launchAmi=ami-57d54d6d

https://console.aws.amazon.com/ec2/home?region=ap-northeast-1#launchAmi=ami-6b4a376a

https://console.aws.amazon.com/ec2/home?region=sa-east-1#launchAmi=ami-15da7808


http://www.datastax.com/dev/blog/what-is-the-story-with-aws-storage

http://www.datastax.com/dev/blog/ec2-series-doc


40

Option Description

--totalnodes#_nodes

Required. The total number of nodes in the cluster.

--versioncommunity

Required. The version of the cluster. Use community to install the latestversion of DataStax Community.

--opscenter [no] Optional. By default, DataStax OpsCenter is installed on the first instance.Specify no to disable.

--reflector url Optional. Allows you to use your own reflector. Default: http://reflector2.datastax.com/reflector2.php

For example: --clustername myDSCcluster --totalnodes 6 --version community

4. Click Next: Add Storage, and add volumes as needed.

The number of instance store devices available to the machine depends on the instance type. EBSvolumes are not recommended for database storage.

5. Click Next: Tag Instance and give a name to your DSE instance, such as workload-dsc.

Tags enable you to categorize your AWS resources in different ways, such as purpose, owner, orenvironment.

6. Click Next: Configure Security Group and configure as follows:

a) Choose Select an existing security group.b) Select the Security Group you created earlier.c) Click Review and Launch.

7. On the Step 7: Review Instance Launch page, make any needed changes.

8. Click Launch and then in the Select an existing key pair or create a new key pair dialog, do one ofthe following:

• Select an existing key pair from the Select a key pair drop list.• If you need to create a new key pair, click Choose an existing key pair drop list and select Create

a new key pair. Then create the new key pair as described in Create key pair.

9. Click Launch Instances.

The AMI image configures your cluster and starts Cassandra services. The Launch Status page isdisplayed.

10.Click View Instances.

Connecting to your DataStax Community EC2 instance

About this taskOnce the cluster is launched, you can connect to it from a terminal or SSH client, such as PuTTY. Connectas user ubuntu rather than as root.


41

Procedure

1. If necessary, from the EC2 Dashboard, click Running Instances.

You can connect to any node in the cluster. However, one node (Node0) runs OpsCenter and is theCassandra seed node.

2. To find which instance is Node0:

a) Select an instance.b) Select the Description tab.c) Scroll down the description information until you see AMI launch index.

d) Repeat until you find Node0.

3. To get the public DNS name of a node, select the node you want to connect to, and then click Connect.

4. In Connect To Your Instance, select A standalone SSH client.

5. Copy the Example command line and change the user from root to ubuntu, then paste it into yourSSH client.

The AMI image configures your cluster and starts the Cassandra services.

6. After you have logged into a node and the AMI has completed installing and setting up the nodes, thestatus is displayed:


42

The URL for the OpsCenter is displayed when you connect to the node containing it; otherwise it is notdisplayed.

7. If you installed OpsCenter, allow 60 to 90 seconds after the cluster has finishedinitializing for OpsCenter to start. You can launch OpsCenter using the URL:http://public_dns_of_first_instance:8888/

The Dashboard should show that the agents are connected.

8. If the agents have not automatically connected:

a) Click the Fix link located near the top left of the Dashboard.

b) When prompted for credentials for the agent nodes, use the username ubuntu and copy and paste

the entire contents from your private key (.pem).

The Dashboard shows the agents are connected.

Expanding a Cassandra AMI cluster

About this task

The best way to expand your EC2 implementations is to use OpsCenter:

• Provisioning a new cluster• Adding an existing cluster• Adding nodes to a cluster

Installing and deploying a Cassandra cluster using GoGridInstalling and deploying a developer (3-node) or production (5-node) Cassandra cluster using GoGrid’s 1-Button Deploy.

About this task

Additional introductory documentation is available from GoGrid at:


/documentation/opscenter/5.0/opsc/online_help/opscAddingCluster_t.html

/documentation/opscenter/5.0/opsc/online_help/opscAddingNode_t.html


43

• GoGrid Cassandra Wiki• Getting Started

The 1-Button Deploy of Cassandra does the following:

• Installs the latest version of Cassandra on X-Large SSD Cloud Servers running Debian 7.2.• Installs OpsCenter.• Installs Oracle JDK 7.• Installs Python Driver.• Enables the Firewall Service - All services are blocked except SSH (22) and ping for public traffic.• Deploys Cassandra using virtual nodes (vnodes).

Procedure

1. Register with GoGrid.

2. Fill out the registration form and complete the account verification.

3. Access the management console with the login credentials you received in your email.

Your cluster automatically starts deploying. A green status indicator shows that a server is up andrunning.

Hover over any item to view its details or right-click to display a context menu.

4. Login to one of the servers and validate that the servers are configured and communicating:

Note: You can login to any member of the cluster either with SSH, a third-party client (likePuTTY), or through the GoGrid Console service.

a) To find your server credentials, right-click the server and select Passwords.b) From your secure connection client, login to the server with the proper credentials. For example from

SSH:

$ ssh root@ip_addressc) Validate that the cluster is running:

$ nodestool status

Each node should be listed and it's status and state should be UN (Up Normal):

https://wiki.gogrid.com/index.php/Big_Data:Cassandra

https://wiki.gogrid.com/index.php/Getting_Started_Guide

http://go.gogrid.com/cassandratrial

https://my.gogrid.com/


44

Datacenter: datacenter1 ======================= Status=Up/Down |/ State=Normal/Leaving/Joining/Moving -- Address Load Tokens Owns (effective) Host ID Rack UN 10.110.94.2 71.46 KB 256 65.9% 3ed072d6-49cb-4713-bd55-ea4de25576a9 rack1 UN 10.110.94.5 40.91 KB 256 66.7% d5d982bc-6e30-40a0-8fe7-e46d6622c1d5 rack1 UN 10.110.94.4 73.33 KB 256 67.4% f6c3bf08-d9e5-43c8-85fa-5420db785052 rack1

What to do next

The following provides information about using and configuring Cassandra, OpsCenter, GoGrid, and theCassandra Query Language (CQL):

• About Apache Cassandra• OpsCenter documentation• GoGrid documentation• CQL for Cassandra 2.x

Installing the Oracle JREInstructions for various platforms.

Installing Oracle JRE on RHEL-based Systems

About this task

You must configure your operating system to use the Oracle JRE, not the OpenJDK. The latest 64-bitversion of Java 7 is recommended. The minimum supported version is 1.7.0_25.

Note: After installing the JRE, you may need to set JAVA_HOME to your profile:

For shell or bash: export JAVA_HOME=path_to_java_home

For csh (C shell): setenv JAVA_HOME=path_to_java_home

Procedure

1. Check which version of the JRE your system is using:

$ java -version

If Oracle Java is used, the results should look like:

java version "1.7.0_25"Java(TM) SE Runtime Environment (build 1.7.0_25-b15)Java HotSpot(TM) 64-Bit Server VM (build 23.25-b01, mixed mode)

2. If necessary, go to Oracle Java SE Downloads, accept the license agreement, and download theinstaller for your distribution.

Note: If installing the Oracle JRE in a cloud environment, accept the license agreement,download the installer to your local client, and then use scp (secure copy) to transfer the file toyour cloud machines.

3. From the directory where you downloaded the package, run the install:

$ sudo rpm -ivh jre-7uversion-linux-x64.rpm

The RPM installs the JRE into the /usr/java/ directory.

/documentation/latest-opsc/

https://wiki.gogrid.com/index.php/Main_Page


http://www.oracle.com/technetwork/java/javase/downloads/index.html


45

4. Use the alternatives command to add a symbolic link to the Oracle JRE installation so that yoursystem uses the Oracle JRE instead of the OpenJDK JRE:

$ sudo alternatives --install /usr/bin/java java /usr/java/jre1.7.0_version/bin/java 200000

If you have any problems, set the PATH and JAVA_HOME variables:

export PATH="$PATH:/usr/java/latest/bin"set JAVA_HOME=/usr/java/latest

5. Make sure your system is now using the correct JRE. For example:

$ java -version


6. If the OpenJDK JRE is still being used, use the alternatives command to switch it. For example:

$ sudo alternatives --config java

There are 2 programs which provide java.

Selection Command------------------------------------------------------------ 1 /usr/lib/jvm/jre-1.7.0-openjdk.x86_64/bin/java*+ 2 /usr/java/jre1.7.0_25/bin/java

Enter to keep the current selection [+ ], or type selection number:

Installing Oracle JRE on Debian or Ubuntu Systems

About this task

You must configure your operating system to use the Oracle JRE, not the OpenJDK. The latest 64-bitversion of Java 7 is recommended. The minimum supported version is 1.7.0_25.

Note: After installing the JRE, you may need to set JAVA_HOME to your profile:

For shell or bash: export JAVA_HOME=path_to_java_home

For csh (C shell): setenv JAVA_HOME=path_to_java_home

About this taskThe Oracle Java Runtime Environment (JRE) has been removed from the official software repositories ofUbuntu and only provides a binary (.bin) version. You can get the JRE from the Java SE Downloads.

Procedure

1. Check which version of the JRE your system is using:

$ java -version

If Oracle Java is used, the results should look like:


2. If necessary, go to Oracle Java SE Downloads, accept the license agreement, and download theinstaller for your distribution.

Note: If installing the Oracle JRE in a cloud environment, accept the license agreement,download the installer to your local client, and then use scp (secure copy) to transfer the file toyour cloud machines.




46

3. Make a directory for the JRE:

$ sudo mkdir -p /usr/lib/jvm

4. Unpack the tarball and install the JRE:

$ sudo tar zxvf jre-7u25-linux-x64.tar.gz -C /usr/lib/jvm

The JRE files are installed into a directory called /usr/lib/jvm/jre-7u_version.

5. Tell the system that there's a new Java version available:

$ sudo update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/jre1.7.0_version/bin/java" 1

If updating from a previous version that was removed manually, execute the above command twice,because you'll get an error message the first time.

6. Set the new JRE as the default:

$ sudo update-alternatives --set java /usr/lib/jvm/jre1.7.0_version/bin/java

7. Make sure your system is now using the correct JRE. For example:

$ java -version


Recommended production settingsRecommendations for production environments; adjust them accordingly for your implementation.

Disable zone_reclaim_mode on NUMA systemsThe Linux kernel can be inconsistent in enabling/disabling zone_reclaim_mode. This can result in oddperformance problems.

To ensure that zone_reclaim_mode is disabled:

$ echo 0 > /proc/sys/vm/zone_reclaim_mode

For more information, see Peculiar Linux kernel performance problem on NUMA systems.

User resource limits

You can view the current limits using the ulimit -a command. Although limits can also be temporarilyset using this command, DataStax recommends making the changes permanent:

Packaged installs: Ensure that the following settings are included in the /etc/security/limits.d/cassandra.conf file:

cassandra - memlock unlimitedcassandra - nofile 100000cassandra - nproc 32768cassandra - as unlimited

Tarball installs: Ensure that the following settings are included in the /etc/security/limits.conf file:

* - memlock unlimited* - nofile 100000* - nproc 32768* - as unlimited

If you run Cassandra as root, some Linux distributions such as Ubuntu, require setting the limits for rootexplicitly instead of using *:

root - memlock unlimited


47

root - nofile 100000root - nproc 32768root - as unlimited

For CentOS, RHEL, OEL systems, also set the nproc limits in /etc/security/limits.d/90-nproc.conf:

* - nproc 32768

For all installations, add the following line to /etc/sysctl.conf:

vm.max_map_count = 131072

To make the changes take effect, reboot the server or run the following command:

$ sudo sysctl -p

To confirm the limits are applied to the Cassandra process, run the following command where pid is theprocess ID of the currently running Cassandra process:

$ cat /proc/<pid>/limits

For more information, see Insufficient user resource limits errors.

Disable swap

You must disable swap entirely. Failure to do so can severely lower performance. Because Cassandrahas multiple replicas and transparent failover, it is preferable for a replica to be killed immediately whenmemory is low rather than go into swap. This allows traffic to be immediately redirected to a functioningreplica instead of continuing to hit the replica that has high latency due to swapping. If your system has alot of DRAM, swapping still lowers performance significantly because the OS swaps out executable codeso that more DRAM is available for caching disks.

If you insist on using swap, you can set vm.swappiness=1. This allows the kernel swap out the absoluteleast used parts.

$ sudo swapoff --all

To make this change permanent, remove all swap file entries from /etc/fstab.

For more information, see Nodes seem to freeze after some period of time.

Synchronize clocks

The clocks on all nodes should be synchronized. You can use NTP (Network Time Protocol) or othermethods.

This is required because columns are only overwritten if the timestamp in the new version of the column ismore recent than the existing column.

Optimum blockdev --setra settings for RAID

Typically, a readahead of 128 is recommended, especially on Amazon EC2 RAID0 devices.

Check to ensure setra is not set to 65536:

$ sudo blockdev --report /dev/<device>

To set setra:

$ sudo blockdev --setra 128 /dev/<device>


48

Java Virtual Machine

The latest 64-bit version of Java 7 is recommended, not the OpenJDK.

Initializing a cluster

49


Initializing a multiple node cluster (single data center)You can initialize a Cassandra cluster with a single data center.

About this task

If you're new to Cassandra, and haven't set up a cluster, see the Getting Started guide or 10 MinuteCassandra Walkthrough.

Before you beginEach node must be correctly configured before starting the cluster. You must determine or perform thefollowing before starting the cluster:

• A good understanding of how Cassandra works. Be sure to read at least Understanding thearchitecture, Data replication, and Cassandra's rack feature.

• Install Cassandra on each node.• Choose a name for the cluster.• Get the IP address of each node.• Determine which nodes will be seed nodes. Do not make all nodes seed nodes. Please read

Internode communications (gossip).• Determine the snitch and replication strategy. The GossipingPropertyFileSnitch and

NetworkTopologyStrategy are recommended for production environments.• If using multiple data centers, determine a naming convention for each data center and rack, for

example: DC1, DC2 or 100, 200 and RAC1, RAC2 or R101, R102. Choose the name carefully;renaming a data center is not possible.

• Other possible configuration settings are described in The cassandra.yaml configuration file andproperty files such as cassandra-rackdc.properties.

About this task

This example describes installing a 6 node cluster spanning 2 racks in a single data center. Each node isconfigured to use the GossipingPropertyFileSnitch and 256 virtual nodes (vnodes).

In Cassandra, the term data center is a grouping of nodes. Data center is synonymous with replicationgroup, that is, a grouping of nodes configured together for replication purposes.

Procedure

1. Suppose you install Cassandra on these nodes:

node0 110.82.155.0 (seed1)node1 110.82.155.1node2 110.82.155.2node3 110.82.156.3 (seed2)node4 110.82.156.4node5 110.82.156.5

Note: It is a best practice to have more than one seed node per data center.

2. If you have a firewall running in your cluster, you must open certain ports for communication betweenthe nodes. See Configuring firewall port access.

3. If Cassandra is running, you must stop the server and clear the data:

/documentation/getting_started/doc/getting_started/gettingStartedCassandraIntro.html

http://planetcassandra.org/Try-Cassandra/



50


Package installations:

a) Stop Cassandra:

$ sudo service cassandra stopb) Clear the data:

$ sudo rm -rf /var/lib/cassandra/data/system/*

Tarball installations:

a) Stop Cassandra:

$ ps auwx | grep cassandra$ sudo kill pid

b) Clear the data:


4. Set the properties in the cassandra.yaml file for each node:

• Package installations: /etc/cassandra/conf/cassandra.yaml• Tarball installations: install_location/conf/cassandra.yaml

Note: After making any changes in the cassandra.yaml file, you must restart the node for thechanges to take effect.

Properties to set:

• num_tokens: recommended value: 256• -seeds: internal IP address of each seed node

Seed nodes do not bootstrap, which is the process of a new node joining an existing cluster. Fornew clusters, the bootstrap process on seed nodes is skipped.

• listen_address:

If not set, Cassandra asks the system for the local address, the one associated with its hostname.In some cases Cassandra doesn't produce the correct address and you must specify thelisten_address.

• endpoint_snitch: name of snitch (See endpoint_snitch.) If you are changing snitches, see Switchingsnitches.

• auto_bootstrap: false (Add this setting only when initializing a fresh cluster with no data.)

Note: If the nodes in the cluster are identical in terms of disk layout, shared libraries, and so on,you can use the same copy of the cassandra.yaml file on all of them.

Example:

cluster_name: 'MyCassandraCluster'num_tokens: 256seed_provider: - class_name: org.apache.cassandra.locator.SimpleSeedProvider parameters: - seeds: "110.82.155.0,110.82.155.3"listen_address:rpc_address: 0.0.0.0endpoint_snitch: GossipingPropertyFileSnitch

5. In the cassandra-rackdc.properties file, assign the data center and rack names you determinedin the Prerequisites. For example:

# indicate the rack and dc for this nodedc=DC1


51

rack=RAC1

6. After you have installed and configured Cassandra on all nodes, start the seed nodes one at a time,and then start the rest of the nodes.

Note: If the node has restarted because of automatic restart, you must first stop the node andclear the data directories, as described above.


$ sudo service cassandra start


$ cd install_location $ bin/cassandra

7. To check that the ring is up and running, run:


$ nodetool status


$ cd install_location $ bin/nodetool status

Each node should be listed and it's status and state should be UN (Up Normal).

Initializing a multiple node cluster (multiple data centers)You can initialize a Cassandra cluster with multiple data centers.

About this task

If you're new to Cassandra, and haven't set up a cluster, see the Getting Started guide or 10 MinuteCassandra Walkthrough.

This example describes installing a six node cluster spanning two data centers. Each node is configured touse the GossipingPropertyFileSnitch (multiple rack aware) and 256 virtual nodes (vnodes).

In Cassandra, the term data center is a grouping of nodes. Data center is synonymous with replicationgroup, that is, a grouping of nodes configured together for replication purposes.

Before you beginEach node must be correctly configured before starting the cluster. You must determine or perform thefollowing before starting the cluster:

• A good understanding of how Cassandra works. Be sure to read at least Understanding thearchitecture, Data replication, and Cassandra's rack feature.

• Install Cassandra on each node.

/documentation/getting_started/doc/getting_started/gettingStartedCassandraIntro.html




52

• Choose a name for the cluster.• Get the IP address of each node.• Determine which nodes will be seed nodes. Do not make all nodes seed nodes. Please read

Internode communications (gossip).• Determine the snitch and replication strategy. The GossipingPropertyFileSnitch and

NetworkTopologyStrategy are recommended for production environments.• If using multiple data centers, determine a naming convention for each data center and rack, for

example: DC1, DC2 or 100, 200 and RAC1, RAC2 or R101, R102. Choose the name carefully;renaming a data center is not possible.

• Other possible configuration settings are described in The cassandra.yaml configuration file andproperty files such as cassandra-rackdc.properties.

Procedure

1. Suppose you install Cassandra on these nodes:

node0 10.168.66.41 (seed1)node1 10.176.43.66node2 10.168.247.41node3 10.176.170.59 (seed2)node4 10.169.61.170node5 10.169.30.138

Note: It is a best practice to have more than one seed node per data center.

2. If you have a firewall running in your cluster, you must open certain ports for communication betweenthe nodes. See Configuring firewall port access.

3. If Cassandra is running, you must stop the server and clear the data:



a) Stop Cassandra:

$ sudo service cassandra stopb) Clear the data:



a) Stop Cassandra:


b) Clear the data:


4. Set the properties in the cassandra.yaml file for each node:

• Package installations: /etc/cassandra/conf/cassandra.yaml• Tarball installations: install_location/conf/cassandra.yaml

Note: After making any changes in the cassandra.yaml file, you must restart the node for thechanges to take effect.

Properties to set:

• num_tokens: recommended value: 256• -seeds: internal IP address of each seed node


53

Seed nodes do not bootstrap, which is the process of a new node joining an existing cluster. Fornew clusters, the bootstrap process on seed nodes is skipped.

• listen_address:

If not set, Cassandra asks the system for the local address, the one associated with its hostname.In some cases Cassandra doesn't produce the correct address and you must specify thelisten_address.

• endpoint_snitch: name of snitch (See endpoint_snitch.) If you are changing snitches, see Switchingsnitches.

• auto_bootstrap: false (Add this setting only when initializing a fresh cluster with no data.)

Note: If the nodes in the cluster are identical in terms of disk layout, shared libraries, and so on,you can use the same copy of the cassandra.yaml file on all of them.

Example:

cluster_name: 'MyCassandraCluster'num_tokens: 256seed_provider: - class_name: org.apache.cassandra.locator.SimpleSeedProvider parameters: - seeds: "10.168.66.41,10.176.170.59"listen_address:endpoint_snitch: GossipingPropertyFileSnitch

Note: Include at least one node from each data center.

5. In the cassandra-rackdc.properties file, assign the data center and rack names you determinedin the Prerequisites. For example:

Nodes 0 to 2

# indicate the rack and dc for this nodedc=DC1rack=RAC1

Nodes 3 to 5

# indicate the rack and dc for this nodedc=DC2rack=RAC1

6. After you have installed and configured Cassandra on all nodes, start the seed nodes one at a time,and then start the rest of the nodes.

Note: If the node has restarted because of automatic restart, you must first stop the node andclear the data directories, as described above.





7. To check that the ring is up and running, run:


$ nodetool status


$ cd install_location


54

$ bin/nodetool status

Each node should be listed and it's status and state should be UN (Up Normal).

Security

55

Security

Securing Cassandra

Cassandra provides these security features to the open source community.

• Client-to-node encryption

Cassandra includes an optional, secure form of communication from a client machine to a databasecluster. Client to server SSL ensures data in flight is not compromised and is securely transferred back/forth from client machines.

• Authentication based on internally controlled login accounts/passwords

Administrators can create users who can be authenticated to Cassandra database clusters using theCREATE USER command. Internally, Cassandra manages user accounts and access to the databasecluster using passwords. User accounts may be altered and dropped using the Cassandra QueryLanguage (CQL).

• Object permission management

Once authenticated into a database cluster using either internal authentication, the next security issueto be tackled is permission management. What can the user do inside the database? Authorizationcapabilities for Cassandra use the familiar GRANT/REVOKE security paradigm to manage objectpermissions.

SSL encryption

Client-to-node encryptionClient-to-node encryption protects data in flight from client machines to a database cluster using SSL(Secure Sockets Layer). It establishes a secure channel between the client and the coordinator node.

Before you beginAll nodes must have all the relevant SSL certificates on all nodes. See Preparing server certificates.

About this task

To enable client-to-node SSL, you must set the client_encryption_options in the cassandra.yaml file.

Procedure

On each node under client_encryption_options:• Enable encryption.• Set the appropriate paths to your .keystore and .truststore files.• Provide the required passwords. The passwords must match the passwords used when generating the

keystore and truststore.• To enable client certificate authentication, set require_client_auth to true. (Available starting with

Cassandra 1.2.3.)

Example

client_encryption_options:enabled: truekeystore: conf/.keystore ## The path to your .keystore file

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56

keystore_password: <keystore password> ## The password you used when generating the keystore.truststore: conf/.truststoretruststore_password: <truststore password>require_client_auth: <true or false>

Node-to-node encryptionNode-to-node encryption protects data transferred between nodes in a cluster, including gossipcommunications, using SSL (Secure Sockets Layer).

Before you beginAll nodes must have all the relevant SSL certificates on all nodes. See Preparing server certificates.

About this task

To enable node-to-node SSL, you must set the server_encryption_options in the cassandra.yaml file.

Procedure

On each node under sever_encryption_options:• Enable internode_encryption.

The available options are:

• all• none• dc: Cassandra encrypts the traffic between the data centers.• rack: Cassandra encrypts the traffic between the racks.

• Set the appropriate paths to your .keystore and .truststore files.• Provide the required passwords. The passwords must match the passwords used when generating the

keystore and truststore.• To enable client certificate authentication, set require_client_auth to true. (Available starting with

Cassandra 1.2.3.)

Example

server_encryption_options: internode_encryption: <internode_option> keystore: resources/dse/conf/.keystore keystore_password: <keystore password> truststore: resources/dse/conf/.truststore truststore_password: <truststore password> require_client_auth: <true or false>

Using cqlsh with SSL encryption

About this task

Using a cqlshrc file means you don't have to override the SSL_CERTFILE environmental variables everytime.

Procedure

1. To run cqlsh with SSL encryption, create a .cassandra/cqlshrc file in your home or client programdirectory.

Sample files are available in the following directories:

Security

57

• Package installations: /etc/cassandra• Tarball installations: install_location/conf

2. Start cqlsh with the --ssl option.

$ cqlsh --ssl ## Package installations$ install_location/bin/cqlsh -ssl ## Tarball installations

Example

[authentication]username = fredpassword = !!bang!!$

[connection]hostname = 127.0.0.1port = 9042

[ssl]certfile = ~/keys/cassandra.certvalidate = true ## Optional, true by defaultuserkey = ~/key.pem ## Provide when require_client_auth=trueusercert = ~/cert.pem ## Provide when require_client_auth=true

[certfiles] ## Optional section, overrides the default certfile in the [ssl] section192.168.1.3 = ~/keys/cassandra01.cert192.168.1.4 = ~/keys/cassandra02.cert

Note: When validate is enabled, the host in the certificate is compared to the host of the machinethat it is connected to. The SSL certificate must be provided either in the configuration file or as anenvironment variable. The environment variables (SSL_CERTFILE and SSL_VALIDATE) overrideany options set in this file.

Preparing server certificatesGenerate SSL certificates for client-to-node encryption or node-to-node encryption.

About this task

If you generate the certificates for one type of encryption, you do not need to generate them again for theother: the same certificates are used for both.

All nodes must have all the relevant SSL certificates on all nodes. A keystore contains private keys. Thetruststore contains SSL certificates for each node and doesn't require signing by a trusted and recognizedpublic certification authority.

Procedure

1. Generate the private and public key pair for the nodes of the cluster.

A prompt for the new keystore and key password appears.

2. Leave key password the same as the keystore password.

3. Repeat steps 1 and 2 on each node using a different alias for each one.

keytool -genkey -keyalg RSA -alias <cassandra_node0> -keystore .keystore

4. Export the public part of the certificate to a separate file and copy these certificates to all other nodes.

keytool -export -alias cassandra -file cassandranode0.cer -keystore .keystore


Security

58

5. Add the certificate of each node to the truststore of each node, so nodes can verify the identity of othernodes.

keytool -import -v -trustcacerts -alias <cassandra_node0> -file <cassandra_node0>.cer -keystore .truststorekeytool -import -v -trustcacerts -alias <cassandra_node1> -file <cassandra_node1>.cer -keystore .truststore. . .

6. Distribute the .keystore and .truststore files to all Cassandra nodes.

7. Make sure .keystore is readable only to the Cassandra daemon and not by any user of the system.

Adding new trusted usersAdd new users when client certificate authentication is enabled.

Before you beginThe client certificate authentication must be enabled (require_client_auth=true).

Procedure

1. Generate the certificate as described in Client-to-node encryption.

2. Import the user's certificate into every node's truststore using keytool:

keytool -import -v -trustcacerts -alias <username> -file <certificate file> -keystore .truststore

Internal authentication

Internal authentication

Like object permission management using internal authorization, internal authentication is based onCassandra-controlled login accounts and passwords. Internal authentication works for the following clientswhen you provide a user name and password to start up the client:

• Astyanax• cassandra-cli• cqlsh• DataStax drivers - produced and certified by DataStax to work with Cassandra.• Hector• pycassa

Internal authentication stores usernames and bcrypt-hashed passwords in the system_auth.credentialstable.

PasswordAuthenticator is an IAuthenticator implementation that you can use to configure Cassandra forinternal authentication out-of-the-box.

Configuring authentication

About this task

To configure Cassandra to use internal authentication, first make a change to the cassandra.yaml file andincrease the replication factor of the system_auth keyspace, as described in this procedure. Next, start upCassandra using the default user name and password (cassandra/cassandra), and start cqlsh using thesame credentials. Finally, use these CQL statements to set up user accounts to authorize users to accessthe database objects:

• ALTER USER

http://www.datastax.com/download#dl-datastax-drivers

/documentation/cql/3.1/cql/cql_reference/alter_user_r.html

Security

59

• CREATE USER• DROP USER• LIST USERS

Note: To configure authorization, see Configuring internal authorization.

Procedure

1. Change the authenticator option in the cassandra.yaml file to PasswordAuthenticator.

By default, the authenticator option is set to AllowAllAuthenticator.

authenticator: PasswordAuthenticator

2. Increase the replication factor for the system_auth keyspace to N (number of nodes).

If you use the default, 1, and the node with the lone replica goes down, you will not be able to log intothe cluster because the system_auth keyspace was not replicated.

3. Restart the Cassandra client.

The default superuser name and password that you use to start the client is stored in Cassandra.

<client startup string> -u cassandra -p cassandra

4. Start cqlsh using the superuser name and password.

./cqlsh -u cassandra -p cassandra

5. Create another superuser, not named cassandra. This step is optional but highly recommended.

6. Log in as that new superuser.

7. Change the cassandra user password to something long and incomprehensible, and then forget aboutit. It won't be used again.

8. Take away the cassandra user's superuser status.

9. Use the CQL statements listed previously to set up user accounts and then grant permissions to accessthe database objects.

Logging in using cqlsh

About this task

Typically, after configuring authentication, you log into cqlsh using the -u and -p options to the cqlshcommand. To avoid having enter credentials every time you launch cqlsh, you can create a cqlshrc filein the .cassandra directory, which is in your home directory. When present, this file passes default logininformation to cqlsh.

Procedure

1. Open a text editor and create a file that specifies a user name and password.

[authentication]username = fredpassword = !!bang!!$

2. Save the file in your home/.cassandra directory and name it cqlshrc.

3. Set permissions on the file.

To protect database login information, ensure that the file is secure from unauthorized access.

Note: Sample cqlshrc files are available in:

• Packaged installations

/usr/share/doc/dse-libcassandra• Binary installations

install_location/conf

/documentation/cql/3.1/cql/cql_reference/create_user_r.html

/documentation/cql/3.1/cql/cql_reference/drop_user_r.html

/documentation/cql/3.1/cql/cql_reference/list_users_r.html

/documentation/cql/3.1/cql/cql_using/update_ks_rf_t.html

Security

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Internal authorization

Object permissions

You use familiar relational database GRANT/REVOKE paradigm to grant or revoke permissions to accessCassandra data. A superuser grants initial permissions, and subsequently a user may or may not begiven the permission to grant/revoke permissions. Object permission management is based on internalauthorization.

Read access to these system tables is implicitly given to every authenticated user because the tables areused by most Cassandra tools:

• system.schema_keyspace• system.schema_columns• system.schema_columnfamilies• system.local• system.peers

Configuring internal authorization

About this task

CassandraAuthorizer is one of many possible IAuthorizer implementations, and the one that storespermissions in the system_auth.permissions table to support all authorization-related CQL statements.Configuration consists mainly of changing the authorizer option in the cassandra.yaml to use theCassandraAuthorizer.

Note: To configure authentication, see Configuring authentication.

Procedure

1. In the cassandra.yaml file, comment out the default AllowAllAuthorizer and add theCassandraAuthorizer.

authorizer: CassandraAuthorizer

You can use any authenticator except AllowAll.

2. Configure the replication factor for the system_auth keyspace to increase the replication factor to anumber greater than 1.

3. Adjust the validity period for permissions caching by setting the permissions_validity_in_ms option inthe cassandra.yaml file.

Alternatively, disable permission caching by setting this option to 0.

ResultsCQL supports these authorization statements:

• GRANT• LIST PERMISSIONS• REVOKE

/documentation/cql/3.1/cql/cql_using/update_ks_rf_t.html

/documentation/cql/3.1/cql/cql_reference/grant_r.html

/documentation/cql/3.1/cql/cql_reference/list_permissions_r.html

/documentation/cql/3.1/cql/cql_reference/revoke_r.html

Security

61

Configuring firewall port accessWhich ports to open when nodes are protected by a firewall.

If you have a firewall running on the nodes in your Cassandra cluster, you must open up the following portsto allow communication between the nodes, including certain Cassandra ports. If this isn’t done, whenyou start Cassandra on a node, the node acts as a standalone database server rather than joining thedatabase cluster.

Table 2: Public ports

Portnumber

Description

22 SSH port

8888 OpsCenter website. The opscenterd daemon listenson this port for HTTP requests coming directly fromthe browser.

Table 3: Cassandra inter-node ports

Portnumber

Description

7000 Cassandra inter-node cluster communication.

7001 Cassandra SSL inter-node cluster communication.

7199 Cassandra JMX monitoring port.

Table 4: Cassandra client ports

Portnumber

Description

9042 Cassandra client port.

9160 Cassandra client port (Thrift).

Table 5: Cassandra OpsCenter ports

Portnumber

Description

61620 OpsCenter monitoring port. The opscenterd daemonlistens on this port for TCP traffic coming from theagent.

61621 OpsCenter agent port. The agents listen on this portfor SSL traffic initiated by OpsCenter.

Database internals

62

Database internals

Storage engine

Cassandra uses a storage structure similar to a Log-Structured Merge Tree, unlike a typical relationaldatabase that uses a B-Tree. Cassandra avoids reading before writing. Read-before-write, especially ina large distributed system, can produce stalls in read performance and other problems. For example, twoclients read at the same time, one overwrites the row to make update A, and then the other overwrites therow to make update B, removing update A. Reading before writing also corrupts caches and increasesIO requirements. To avoid a read-before-write condition, the storage engine groups inserts/updates to bemade, and sequentially writes only the updated parts of a row in append mode. Cassandra never re-writesor re-reads existing data, and never overwrites the rows in place.

A log-structured engine that avoids overwrites and uses sequential IO to update data is essential for writingto hard disks (HDD) and solid-state disks (SSD). On HDD, writing randomly involves a higher number ofseek operations than sequential writing. The seek penalty incurred can be substantial. Using sequentialIO, and thereby avoiding write amplification and disk failure, Cassandra accommodates inexpensive,consumer SSDs extremely well.

Separate table directories

Cassandra provides fine-grained control of table storage on disk, writing tables to disk using separatedirectories for each table. From the installation directory, data files are stored using this directory and filenaming format on default tarball installations:

/data/data/ks1/cf1-5be396077b811e3a3ab9dc4b9ac088d/ks1-cf1-hc-1-Data.db

On packaged installations, the data files are stored in the same format, but in /var/lib/cassandra/data by default. In this example, ks1 represents the keyspace name to distinguish the keyspace forstreaming or bulk loading data. A hexadecimal string, 5be396077b811e3a3ab9dc4b9ac088d in thisexample, is appended to table names to represent unique table IDs.

Cassandra creates a subdirectory for each table, which allows you to symlink a table to a chosen physicaldrive or data volume. This provides the capability to move very active tables to faster media, such asSSD’s for better performance, and also divvy up tables across all attached storage devices for better I/Obalance at the storage layer.

Cassandra storage basics

To manage and access data in Cassandra, it is important to understand how Casssandra stores data. Thehinted handoff feature and Cassandra conformance and non-conformance to the ACID (atomic, consistent,isolated, durable) database properties are key concepts in this discussion. In Cassandra, consistencyrefers to how up-to-date and synchronized a row of data is on all of its replicas.

Client utilities and application programming interfaces (APIs) for developing applications for data storageand retrieval are available.

The write path to compaction

Cassandra processes data at several stages on the write path, starting with the immediate logging of awrite and ending in compaction:

http://en.wikipedia.org/wiki/Write_amplification

Database internals

63

• Logging data in the commit log• Writing data to the memtable• Flushing data from the memtable• Storing data on disk in SSTables• Compaction

Logging writes and memtable storage

When a write occurs, Cassandra stores the data in a structure in memory, the memtable, and alsoappends writes to the commit log on disk, providing configurable durability. The commit log receives everywrite made to a Cassandra node, and these durable writes survive permanently even after power failure.The memtable is a write-back cache of data partitions that Cassandra looks up by key. The memtablestores writes until reaching a limit, and then is flushed.

Flushing data from the memtable

When memtable contents exceed a configurable threshold, the memtable data, which includesindexes, is put in a queue to be flushed to disk. You can configure the length of the queue by changingmemtable_flush_queue_size in the cassandra.yaml. If the data to be flushed exceeds the queue size,Cassandra blocks writes until the next flush succeeds. You can manually flush a table using the nodetoolflush command. Typically, before restarting nodes, flushing the memtable is recommended to reducecommit log replay time. To flush the data, Cassandra sorts memtables by token and then writes the data todisk sequentially.

Storing data on disk in SSTables

Data in the commit log is purged after its corresponding data in the memtable is flushed to an SSTable.

Memtables and SSTables are maintained per table. SSTables are immutable, not written to again after thememtable is flushed. Consequently, a partition is typically stored across multiple SSTable files.

For each SSTable, Cassandra creates these structures:

• Partition index

A list of partition keys and the start position of rows in the data file (on disk)• Partition summary (in memory)

A sample of the partition index.• Bloom filter

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Compaction

Periodic compaction is essential to a healthy Cassandra database because Cassandra does not insert/update in place. As inserts/updates occur, instead of overwriting the rows, Cassandra writes a newtimestamped version of the inserted or updated data in another SSTable. Cassandra manages theaccumulation of SSTables on disk using compaction.

Cassandra also does not delete in place because the SSTable is immutable. Instead, Cassandra marksdata to be deleted using a tombstone. Tombstones exist for a configured time period defined by thegc_grace_seconds value set on the table.

During compaction, there is a temporary spike in disk space usage and disk I/O because the old and newSSTables co-exist. This diagram depicts the compaction process:

Compaction merges the data in each SSTable by partition key, selecting the latest data for storagebased on its timestamp. Cassandra can merge the data performantly, without random IO, because rowsare sorted by partition key within each SSTable. After evicting tombstones and removing deleted data,columns, and rows, the compaction process consolidates SSTables into a single file. The old SSTablefiles are deleted as soon as any pending reads finish using the files. Disk space occupied by old SSTablesbecomes available for reuse.

Cassandra 2.1 improves read performance after compaction by performing an incremental replacementof compacted SSTables. Instead of waiting for the entire compaction to finish and then throwing away theold SSTable (and cache), Cassandra can read data directly from the new SSTable even before it finisheswriting.

As data is written to the new SSTable and reads are directed to it, the corresponding data in the oldSSTables is no longer accessed and is evicted from the page cache. Thus begins an incremental processof caching the new SSTable, while directing reads away from the old one. The dramatic cache miss isgone. Cassandra provides predictable high performance even under heavy load.

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Starting compaction

You can configure these types of compaction to run periodically:

• SizeTieredCompactionStrategy

For write-intensive workloads• LeveledCompactionStrategy

For read-intensive workloads• DateTieredCompactionStrategy

For time series data and expiring (TTL) data

You can manually start compaction using the nodetool compact command.

For more information about compaction strategies, see When to Use Leveled Compaction and LeveledCompaction in Apache Cassandra.

How Cassandra stores and distributes indexes

Internally, a Cassandra index is a data partition. In the example of a music service, the playlists tableincludes an artist column and uses a compound partition key: id is the partition key and song_order is theclustering column.

CREATE TABLE playlists ( id uuid, song_order int, . . . artist text,PRIMARY KEY (id, song_order ) );

As shown in the music service example, to filter the data based on the artist, create an index on artist.Cassandra uses the index to pull out the records in question. An attempt to filter the data before creatingthe index will fail because the operation would be very inefficient. A sequential scan across the entireplaylists dataset would be required. After creating the artist index, Cassandra can filter the data in theplaylists table by artist, such as Fu Manchu.

The partition is the unit of replication in Cassandra. In the music service example, partitions are distributedby hashing the playlist id and using the ring to locate the nodes that store the distributed data. Cassandrawould generally store playlist information on different nodes, and to find all the songs by Fu Manchu,Cassandra would have to visit different nodes. To avoid these problems, each node indexes its own data.

This technique, however, does not guarantee trouble-free indexing, so know when and when not to use anindex.

About index updates

As with relational databases, keeping indexes up to date is not free, so unnecessary indexes should beavoided. When a column is updated, the index is updated as well. If the old column value was still in thememtable, which typically occurs when updating a small set of rows repeatedly, Cassandra removes thecorresponding obsolete index entry; otherwise, the old entry remains to be purged by compaction. If a readsees a stale index entry before compaction purges it, the reader thread invalidates it.

The write path of an update

Inserting a duplicate primary key is treated as an upsert. Eventually, the updates are streamed to diskusing sequential I/O and stored in a new SSTable. During an update, Cassandra time-stamps andwrites columns to disk using the write path. During the update, if multiple versions of the column existin the memtable, Cassandra flushes only the newer version of the column to disk, as described in theCompaction section.




http://planetcassandra.org/blog/getting-started-with-time-series-data-modeling/

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http://www.datastax.com/dev/blog/when-to-use-leveled-compaction



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About deletes

The way Cassandra deletes data differs from the way a relational database deletes data. A relationaldatabase might spend time scanning through data looking for expired data and throwing it away or anadministrator might have to partition expired data by month, for example, to clear it out faster. Data in aCassandra column can have an optional expiration date called TTL (time to live). Use CQL to set the TTLin seconds for data. Cassandra marks TTL data with a tombstone after the requested amount of time hasexpired. A tombstone exists for gc_grace_seconds. After data is marked with a tombstone, the data isautomatically removed during the normal compaction process.

Facts about deleted data to keep in mind are:

• Cassandra does not immediately remove data marked for deletion from disk. The deletion occurs duringcompaction.

• If you use the size-tiered or date-tiered compaction strategy, you can drop data immediately bymanually starting the compaction process. Before doing so, understand the documented disadvantagesof the process.

• Deleted data can reappear if you do not run node repair routinely.

Why deleted data can reappear

Marking data with a tombstone signals Cassandra to retry sending a delete request to a replica that wasdown at the time of delete. If the replica comes back up within the grace period of time, it eventuallyreceives the delete request. However, if a node is down longer than the grace period, the node can missthe delete because the tombstone disappears after gc_grace_seconds. Cassandra always attempts toreplay missed updates when the node comes back up again. After a failure, it is a best practice to run noderepair to repair inconsistencies across all of the replicas when bringing a node back into the cluster. If thenode doesn't come back within gc_grace,_seconds, remove the node, wipe it, and bootstrap it again.

About hinted handoff writes

Hinted handoff is a Cassandra feature that optimizes the cluster consistency process and anti-entropywhen a replica-owning node is not available, due to network issues or other problems, to accept a replicafrom a successful write operation. Hinted handoff is not a process that guarantees successful writeoperations, except when a client application uses a consistency level of ANY. You enable or disable hintedhandoff in the cassandra.yaml file.

How hinted handoff works

During a write operation, when hinted handoff is enabled and consistency can be met, the coordinatorstores a hint about dead replicas in the local system.hints table under either of these conditions:

• A replica node for the row is known to be down ahead of time.• A replica node does not respond to the write request.

When the cluster cannot meet the consistency level specified by the client, Cassandra does not store ahint.

A hint indicates that a write needs to be replayed to one or more unavailable nodes. The hint consists of:

• The location of the replica that is down• Version metadata• The actual data being written

By default, hints are saved for three hours after a replica fails because if the replica is downlonger than that, it is likely permanently dead. You can configure this interval of time using themax_hint_window_in_ms property in the cassandra.yaml file. If the node recovers after the save time haselapsed, run a repair to re-replicate the data written during the down time.

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After a node discovers from gossip that a node for which it holds hints has recovered, the node sends thedata row corresponding to each hint to the target. Additionally, the node checks every ten minutes for anyhints for writes that timed out during an outage too brief for the failure detector to notice through gossip.

For example, in a cluster of two nodes, A and B, having a replication factor (RF) of 1, each row is stored onone node. Suppose node A is down while we write row K to it with consistency level of one. The write failsbecause reads always reflect the most recent write when:

W + R > replication factor

where W is the number of nodes to block for writes and R is the number of nodes to block for reads.Cassandra does not write a hint to B and call the write good because Cassandra cannot read the data atany consistency level until A comes back up and B forwards the data to A.

In a cluster of three nodes, A (the coordinator), B, and C, each row is stored on two nodes in a keyspacehaving a replication factor of 2. Suppose node C goes down. The client writes row K to node A. Thecoordinator, replicates row K to node B, and writes the hint for downed node C to node A.

Cassandra, configured with a consistency level of ONE, calls the write good because Cassandra can readthe data on node B. When node C comes back up, node A reacts to the hint by forwarding the data to nodeC. For more information about how hinted handoff works, see "Modern hinted handoff" by Jonathan Ellis.

Extreme write availability

For applications that want Cassandra to accept writes even when all the normal replicas are down, whennot even consistency level ONE can be satisfied, Cassandra provides consistency level ANY. ANYguarantees that the write is durable and will be readable after an appropriate replica target becomesavailable and receives the hint replay.

Performance

By design, hinted handoff inherently forces Cassandra to continue performing the same number of writeseven when the cluster is operating at reduced capacity. Pushing your cluster to maximum capacity with noallowance for failures is a bad idea.

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Hinted handoff is designed to minimize the extra load on the cluster.

All hints for a given replica are stored under a single partition key, so replaying hints is a simple sequentialread with minimal performance impact.

If a replica node is overloaded or unavailable, and the failure detector has not yet marked it down, thenexpect most or all writes to that node to fail after the timeout triggered by write_request_timeout_in_ms,which defaults to 10 seconds.

If this happens on many nodes at once this could become substantial memory pressure on the coordinator.So the coordinator tracks how many hints it is currently writing, and if this number gets too high it willtemporarily refuse writes (withOverloadedException) whose replicas include the misbehaving nodes.

Removal of hints

When removing a node from the cluster by decommissioning the node or by using the nodetoolremovenode command, Cassandra automatically removes hints targeting the node that no longer exists.Cassandra also removes hints for dropped tables.

Scheduling repair weekly

At first glance, it seems that hinted handoff eliminates the need for repair, but this is not true becausehardware failure is inevitable and has the following ramifications:

• Loss of the historical data necessary to tell the rest of the cluster exactly what data is missing.• Loss of hints-not-yet-replayed from requests that the failed node coordinated.

About reads

Cassandra must combine results from the active memtable and potentially mutliple SSTables to satisfy aread.

First, Cassandra checks the Bloom filter. Each SSTable has a Bloom filter associated with it that checksthe probability of having any data for the requested partition in the SSTable before doing any disk I/O.

If the Bloom filter does not rule out the SSTable, Cassandra checks the partition key cache and takes oneof these courses of action:

• If an index entry is found in the cache:

• Cassandra goes to the compression offset map to find the compressed block having the data.• Fetches the compressed data on disk and returns the result set.

• If an index entry is not found in the cache:

• Cassandra searches the partition summary to determine the approximate location on disk of theindex entry.

• Next, to fetch the index entry, Cassandra hits the disk for the first time, performing a single seek anda sequential read of columns (a range read) in the SSTable if the columns are contiguous.

• Cassandra goes to the compression offset map to find the compressed block having the data.• Fetches the compressed data on disk and returns the result set.

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How off-heap components affect reads

To increase the data handling capacity per node, Cassandra keeps these components off-heap:

• Bloom filter• Compression offsets map• Partition summary

Of the components in memory, only the partition key cache is a fixed size. Other components grow as thedata set grows.

Bloom filter

The Bloom filter grows to approximately 1-2 GB per billion partitions. In the extreme case, you can haveone partition per row, so you can easily have billions of these entries on a single machine. The Bloom filteris tunable if you want to trade memory for performance.

Partition summary

By default, the partition summary is a sample of the partition index. You configure sample frequencyby changing the index_interval property in the table definition, also if you want to trade memory forperformance.

Compression offsets

The compression offset map grows to 1-3 GB per terabyte compressed. The more you compress data, thegreater number of compressed blocks you have and the larger the compression offset table. Compressionis enabled by default even though going through the compression offset map consumes CPU resources.Having compression enabled makes the page cache more effective, and typically, almost always pays off.

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Reading from a partition

Within a partition, all rows are not equally expensive to query. The very beginning of the partition—thefirst rows, clustered by your key definition—is slightly less expensive to query because there is no need toconsult the partition-level index.

How write patterns affect reads

The type of compaction strategy Cassandra performs on your data is configurable and can significantlyaffect read performance. Using the SizeTieredCompactionStrategy or DateTieredCompactionStrategytends to cause data fragmentation when rows are frequently updated. The LeveledCompactionStrategy(LCS) was designed to prevent fragmentation under this condition. For more information about LCS, seethe article, Leveled Compaction in Apache Cassandra.

How the row cache affects reads

Typical of any database, reads are fastest when the most in-demand data (or hot working set) fits intomemory. Although all modern storage systems rely on some form of caching to allow for fast access tohot data, not all of them degrade gracefully when the cache capacity is exceeded and disk I/O is required.Cassandra's read performance benefits from built-in caching, shown in the following diagram.

The red lines in the SSTables in this diagram are fragments of a row that Cassandra needs to combine togive the user the requested results. Cassandra caches the merged value, not the raw row fragments. Thatsaves some CPU and disk I/O.

The row cache is not write-through. If a write comes in for the row, the cache for it is invalidated and is notcached again until it is read.

For rows that are accessed frequently, Cassandra 2.1 has improved the built-in partition key cache and anoptional row cache.

About transactions and concurrency control

Cassandra does not use RDBMS ACID transactions with rollback or locking mechanisms, but insteadoffers atomic, isolated, and durable transactions with eventual/tunable consistency that lets the user decidehow strong or eventual they want each transaction’s consistency to be.

• Atomic

Everything in a transaction succeeds or the entire transaction is rolled back.• Consistent

A transaction cannot leave the database in an inconsistent state.


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• Isolated

Transactions cannot interfere with each other.• Durable

Completed transactions persist in the event of crashes or server failure.

As a non-relational database, Cassandra does not support joins or foreign keys, and consequently doesnot offer consistency in the ACID sense. For example, when moving money from account A to B the totalin the accounts does not change. Cassandra supports atomicity and isolation at the row-level, but tradestransactional isolation and atomicity for high availability and fast write performance. Cassandra writes aredurable.

Lightweight transactions

Lightweight transactions, also known as compare and set, with linearizable consistency ensure atransaction isolation level similar to the serializable level offered by RDBMS’s. You use lightweighttransactions instead of durable transactions with eventual/tunable consistency for situations the requirenodes in the distributed system to agree on changes to data. For example, two users attempting tocreate a unique user account in the same cluster could overwrite each other’s work. Using a lightweighttransaction, the nodes can agree to create only one account.

Cassandra implements lightweight transactions by extending the Paxos consensus protocol, which isbased on a quorum-based algorithm. Using this protocol, a distributed system can agree on proposed dataadditions/modifications without the need for a master database or two-phase commit.

You use extensions in CQL for lightweight transactions.

You can use an IF clause in a number of CQL statements, such as INSERT, for lightweight transactions.For example, to ensure that an insert into a new accounts table is unique for a new customer, use the IFNOT EXISTS clause:

INSERT INTO customer_account (customerID, customer_email) VALUES (‘LauraS’, ‘[email protected]’)IF NOT EXISTS;

DML modifications you make using UPDATE can also make use of the IF clause by comparing one ormore columns to various values:

UPDATE customer_accountSET customer_email=’[email protected]’IF customerID=’LauraS’;

Cassandra 2.1.1 and later support non-equal conditions for lightweight transactions. You can use <, <=,>, >=, != and IN operators in WHERE clauses to query lightweight tables. Behind the scenes, Cassandrais making four round trips between a node proposing a lightweight transaction and any needed replicasin the cluster to ensure proper execution so performance is affected. Consequently, reserve lightweighttransactions for those situations where they are absolutely necessary; Cassandra’s normal eventualconsistency can be used for everything else.

A SERIAL consistency level allows reading the current (and possibly uncommitted) state of data withoutproposing a new addition or update. If a SERIAL read finds an uncommitted transaction in progress,Cassandra performs a read repair as part of the commit.

Atomicity

In Cassandra, a write is atomic at the partition-level, meaning inserting or updating columns in a row istreated as one write operation. A delete operation is also performed atomically. By default, all operationsin a batch are performed atomically. Cassandra uses a batch log to ensure all operations in a batchare applied atomically. There is a performance penalty for batch atomicity when a batch spans multiplepartitions. If you do not want to incur this penalty, use the UNLOGGED option. Using UNLOGGED makesthe batch operation atomic only within a single partition.

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For example, if using a write consistency level of QUORUM with a replication factor of 3, Cassandra willreplicate the write to all nodes in the cluster and wait for acknowledgement from two nodes. If the write failson one of the nodes but succeeds on the other, Cassandra reports a failure to replicate the write on thatnode. However, the replicated write that succeeds on the other node is not automatically rolled back.

Cassandra uses timestamps to determine the most recent update to a column. The timestamp is providedby the client application. The latest timestamp always wins when requesting data, so if multiple clientsessions update the same columns in a row concurrently, the most recent update is the one that will beseen by readers.

Consistency

Cassandra offers two types of consistency:

• Tunable consistency

Availability and consistency can be tuned, and can be strong in the CAP sense--data is madeconsistent across all the nodes in a distributed database cluster.

• Linearizable consistency

In ACID terms, linearizable consistency is a serial (immediate) isolation level for lightweighttransactions.

In Cassandra, there are no locking or transactional dependencies when concurrently updating multiplerows or tables. Tuning availability and consistency always gives you partition tolerance. A user can pickand choose on a per operation basis how many nodes must receive a DML command or respond to aSELECT query.

For in-depth information about this new consistency level, see the article, Lightweight transactions inCassandra.

To support linearizable consistency, a consistency level of SERIAL has been added to Cassandra.Additions to CQL have been made to support lightweight transactions.

Isolation

In early versions of Cassandra, it was possible to see partial updates in a row when one user was updatingthe row while another user was reading that same row. For example, if one user was writing a row with twothousand columns, another user could potentially read that same row and see some of the columns, butnot all of them if the write was still in progress.

Full row-level isolation is in place, which means that writes to a row are isolated to the client performingthe write and are not visible to any other user until they are complete. Delete operations are performed inisolation. All updates in a batch operation belonging to a given partition key are performed in isolation.

Durability

Writes in Cassandra are durable. All writes to a replica node are recorded both in memory and in a commitlog on disk before they are acknowledged as a success. If a crash or server failure occurs before thememtables are flushed to disk, the commit log is replayed on restart to recover any lost writes. In additionto the local durability (data immediately written to disk), the replication of data on other nodes strengthensdurability.

You can manage the local durability to suit your needs for consistency using the commitlog_sync option inthe cassandra.yaml file. Set the option to either periodic or batch.

http://www.cs.berkeley.edu/~brewer/cs262b-2004/PODC-keynote.pdf

http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0

http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0

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About data consistency

Consistency refers to how up-to-date and synchronized a row of Cassandra data is on all of its replicas.Cassandra extends the concept of eventual consistency by offering tunable consistency. For any givenread or write operation, the client application decides how consistent the requested data must be.

A tutorial in the CQL documentation compares consistency levels using cqlsh tracing.

Even at low consistency levels, Cassandra writes to all replicas of the partition key, even replicas in otherdata centers. The consistency level determines only the number of replicas that need to acknowledgethe write success to the client application. Typically, a client specifies a consistency level that is less thanthe replication factor specified by the keyspace. This practice ensures that the coordinating server nodereports the write successful even if some replicas are down or otherwise not responsive to the write.

The read consistency level specifies how many replicas must respond to a read request before returningdata to the client application. Cassandra checks the specified number of replicas for data to satisfy theread request.

About built-in consistency repair features

You can use these built-in repair utilities to ensure that data remains consistent across replicas.

• Read repair• Hinted handoff• Anti-entropy node repair

Configuring data consistency

Consistency levels in Cassandra can be configured to manage availability versus data accuracy. Youcan configure consistency on a cluster, data center, or individual I/O operation basis. Consistency amongparticipating nodes can be set globally and also controlled on a per-operation basis (for example insert orupdate) using Cassandra’s drivers and client libraries.

Write consistency levels

This table describes the write consistency levels in strongest-to-weakest order.

Table 6: Write Consistency Levels

Level Description Usage

ALL A write must be written to thecommit log and memtable on allreplica nodes in the cluster forthat partition.

Provides the highest consistencyand the lowest availability of anyother level.

EACH_QUORUM Strong consistency. A write mustbe written to the commit log andmemtable on a quorum of replicanodes in all data centers.

Used in multiple data centerclusters to strictly maintainconsistency at the same level ineach data center. For example,choose this level if you want aread to fail when a data center isdown and the QUORUM cannot bereached on that data center.

QUORUM A write must be written to thecommit log and memtable on aquorum of replica nodes.

Provides strong consistency ifyou can tolerate some level offailure.

http://en.wikipedia.org/wiki/Eventual_consistency

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LOCAL_QUORUM Strong consistency. A writemust be written to the commitlog and memtable on a quorumof replica nodes in the samedata center as the coordinatornode. Avoids latency of inter-datacenter communication.

Used in multiple data centerclusters with a rack-awarereplica placement strategy (NetworkTopologyStrategy)and a properly configuredsnitch. Fails when usingSimpleStrategy. Use tomaintain consistency locally(within the single data center).

ONE A write must be written to thecommit log and memtable of atleast one replica node.

Satisfies the needs of mostusers because consistencyrequirements are not stringent.

TWO A write must be written to thecommit log and memtable of atleast two replica nodes.

Similar to ONE.

THREE A write must be written to thecommit log and memtable of atleast three replica nodes.

Similar to TWO.

LOCAL_ONE A write must be sent to, andsuccessfully acknowledged by, atleast one replica node in the localdatacenter.

In a multiple data center clusters,a consistency level of ONEis often desirable, but cross-DC traffic is not. LOCAL_ONEaccomplishes this. For securityand quality reasons, you can usethis consistency level in an offlinedatacenter to prevent automaticconnection to online nodes inother data centers if an offlinenode goes down.

ANY A write must be written to at leastone node. If all replica nodes forthe given partition key are down,the write can still succeed after ahinted handoff has been written.If all replica nodes are down atwrite time, an ANY write is notreadable until the replica nodesfor that partition have recovered.

Provides low latency and aguarantee that a write never fails.Delivers the lowest consistencyand highest availability.

SERIAL Achieves linearizable consistencyfor lightweight transactions bypreventing unconditional updates.

You cannot configure this levelas a normal consistency level,configured at the driver levelusing the consistency level field.You configure this level using theserial consistency field as part ofthe native protocol operation. Seefailure scenarios.

LOCAL_SERIAL Same as SERIAL but confined tothe data center. A write must bewritten conditionally to the commitlog and memtable on a quorum

Same as SERIAL. Used fordisaster recovery. See failurescenarios.

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of replica nodes in the same datacenter.

SERIAL and LOCAL_SERIAL write failure scenarios

If one of three nodes is down, the Paxos commit fails under the following conditions:

• CQL query-configured consistency level of ALL• Driver-configured serial consistency level of SERIAL• Replication factor of 3

A WriteTimeout with a WriteType of CAS occurs and further reads do not see the write. If the node goesdown in the middle of the operation instead of before the operation started, the write is committed, thevalue is written to the live nodes, and a WriteTimeout with a WriteType of SIMPLE occurs.

Under the same conditions, if two of the nodes are down at the beginning of the operation, the Paxoscommit fails and nothing is committed. If the two nodes go down after the Paxos proposal is accepted,the write is committed to the remaining live nodes and written there, but a WriteTimeout with WriteTypeSIMPLE is returned.

Read consistency levels

This table describes read consistency levels in strongest-to-weakest order.

Table 7: Read Consistency Levels


ALL Returns the record after allreplicas have responded. Theread operation will fail if a replicadoes not respond.

Provides the highest consistencyof all levels and the lowestavailability of all levels.

EACH_QUORUM Returns the record after a quorumof replicas in each data center ofthe cluster has responded.

Same as LOCAL_QUORUM

QUORUM Returns the record after a quorumof replicas has responded fromany data center.

Ensures strong consistency if youcan tolerate some level of failure.

LOCAL_QUORUM Returns the record after a quorumof replicas in the current datacenter as the coordinator nodehas reported. Avoids latency ofinter-data center communication.

Used in multiple data centerclusters with a rack-awarereplica placement strategy (NetworkTopologyStrategy)and a properly configuredsnitch. Fails when usingSimpleStrategy.

ONE Returns a response from theclosest replica, as determinedby the snitch. By default, a readrepair runs in the backgroundto make the other replicasconsistent.

Provides the highest availabilityof all the levels if you can toleratea comparatively high probabilityof stale data being read. Thereplicas contacted for reads maynot always have the most recentwrite.

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TWO Returns the most recent datafrom two of the closest replicas.

Similar to ONE.

THREE Returns the most recent datafrom three of the closest replicas.

Similar to TWO.

LOCAL_ONE Returns a response from theclosest replica in the local datacenter.

Same usage as described in thetable about write consistencylevels.

SERIAL Allows reading the current (andpossibly uncommitted) state ofdata without proposing a newaddition or update. If a SERIALread finds an uncommittedtransaction in progress, it willcommit the transaction as part ofthe read. Similar to QUORUM.

To read the latest value of acolumn after a user has invokeda lightweight transaction to writeto the column, use SERIAL.Cassandra then checks theinflight lightweight transaction forupdates and, if found, returns thelatest data.

LOCAL_SERIAL Same as SERIAL, but confinedto the data center. Similar toLOCAL_QUORUM.

Used to achieve linearizableconsistency for lightweighttransactions.

About the QUORUM levels

The QUORUM level writes to the number of nodes that make up a quorum. A quorum is calculated, and thenrounded down to a whole number, as follows:

quorum = (sum_of_replication_factors / 2) + 1

The sum of all the replication_factor settings for each data center is thesum_of_replication_factors.

sum_of_replication_factors = datacenter1_RF + datacenter2_RF + . . . + datacentern_RF

Examples:

• Using a replication factor of 3, a quorum is 2 nodes. The cluster can tolerate 1 replica down.• Using a replication factor of 6, a quorum is 4. The cluster can tolerate 2 replicas down.• In a two data center cluster where each data center has a replication factor of 3, a quorum is 4 nodes.

The cluster can tolerate 2 replica nodes down.• In a five data center cluster where two data centers have a replication factor of 3 and three data centers

have a replication factor of 2, a quorum is 6 nodes.

The more data centers, the higher number of replica nodes need to respond for a successful operation.

If consistency is a top priority, you can ensure that a read always reflects the most recent write by using thefollowing formula:

(nodes_written + nodes_read) > replication_factor

For example, if your application is using the QUORUM consistency level for both write and read operationsand you are using a replication factor of 3, then this ensures that 2 nodes are always written and 2 nodesare always read. The combination of nodes written and read (4) being greater than the replication factor (3)ensures strong read consistency.

Similar to QUORUM, the LOCAL_QUORUM level is calculated based on the replication factor of the same datacenter as the coordinator node. That is, even if the cluster has more than one data center, the quorum iscalculated only with local replica nodes.

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In EACH_QUORUM, every data center in the cluster must reach a quorum based on that data center'sreplication factor in order for the read or write request to succeed. That is, for every data center in thecluster a quorum of replica nodes must respond to the coordinator node in order for the read or writerequest to succeed.

Configuring client consistency levels

You can use a new cqlsh command, CONSISTENCY, to set the consistency level for queriesfrom the current cqlsh session. The WITH CONSISTENCY clause has been removed from CQLcommands. You set the consistency level programmatically (at the driver level). For example, callQueryBuilder.insertInto with a setConsistencyLevel argument. The consistency level defaultsto ONE for all write and read operations.

Read requests

There are three types of read requests that a coordinator can send to a replica:

• A direct read request• A digest request• A background read repair request

The coordinator node contacts one replica node with a direct read request. Then the coordinator sendsa digest request to a number of replicas determined by the consistency level specified by the client. Thedigest request checks the data in the replica node to make sure it is up to date. Then the coordinatorsends a digest request to all remaining replicas. If any replica nodes have out of date data, a backgroundread repair request is sent. Read repair requests ensure that the requested row is made consistent on allreplicas.

For a digest request the coordinator first contacts the replicas specified by the consistency level. Thecoordinator sends these requests to the replicas that are currently responding the fastest. The nodescontacted respond with a digest of the requested data; if multiple nodes are contacted, the rows from eachreplica are compared in memory to see if they are consistent. If they are not, then the replica that has themost recent data (based on the timestamp) is used by the coordinator to forward the result back to theclient.

To ensure that all replicas have the most recent version of frequently-read data, the coordinator alsocontacts and compares the data from all the remaining replicas that own the row in the background. If thereplicas are inconsistent, the coordinator issues writes to the out-of-date replicas to update the row to themost recent values. This process is known as read repair. Read repair can be configured per table fornon-QUORUM consistency levels (using read_repair_chance), and is enabled by default.

For illustrated examples of read requests, see the examples of read consistency levels.

Rapid read protection using speculative_retry

Rapid read protection allows Cassandra to still deliver read requests when the originally selectedreplica nodes are either down or taking too long to respond. If the table has been configured with thespeculative_retry property, the coordinator node for the read request will retry the request withanother replica node if the original replica node exceeds a configurable timeout value to complete the readrequest.

/documentation/cql/3.1/cql/cql_reference/consistency_r.html


/documentation/cql/3.1/cql/cql_reference/tabProp.html?scroll=tabProp__morespeculativeRetry

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Examples of read consistency levels

The following diagrams show examples of read requests using these consistency levels:

• QUORUM in a single data center• ONE in a single data center• QUORUM in two data centers• LOCAL_QUORUM in two data centers• ONE in two data centers• LOCAL_ONE in two data centers

Rapid read protection diagram shows how the speculative retry table property affects consistency.

A single data center cluster with a consistency level of QUORUM

In a single data center cluster with a replication factor of 3, and a read consistency level of QUORUM, 2of the 3 replicas for the given row must respond to fulfill the read request. If the contacted replicas havedifferent versions of the row, the replica with the most recent version will return the requested data. In thebackground, the third replica is checked for consistency with the first two, and if needed, a read repair isinitiated for the out-of-date replicas.

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A single data center cluster with a consistency level of ONE

In a single data center cluster with a replication factor of 3, and a read consistency level of ONE, theclosest replica for the given row is contacted to fulfill the read request. In the background a read repair ispotentially initiated, based on the read_repair_chance setting of the table, for the other replicas.

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A two data center cluster with a consistency level of QUORUM

In a two data center cluster with a replication factor of 3, and a read consistency of QUORUM, 4 replicas forthe given row must resond to fulfill the read request. The 4 replicas can be from any data center. In thebackground, the remaining replicas are checked for consistency with the first four, and if needed, a readrepair is initiated for the out-of-date replicas.

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A two data center cluster with a consistency level of LOCAL_QUORUM

In a multiple data center cluster with a replication factor of 3, and a read consistency of LOCAL_QUORUM,2 replicas in the same data center as the coordinator node for the given row must respond to fulfill theread request. In the background, the remaining replicas are checked for consistency with the first 2, and ifneeded, a read repair is initiated for the out-of-date replicas.

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A two data center cluster with a consistency level of ONE

In a multiple data center cluster with a replication factor of 3, and a read consistency of ONE, theclosest replica for the given row, regardless of data center, is contacted to fulfill the read request. In thebackground a read repair is potentially initiated, based on the read_repair_chance setting of the table,for the other replicas.

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A two data center cluster with a consistency level of LOCAL_ONE

In a multiple data center cluster with a replication factor of 3, and a read consistency of LOCAL_ONE, theclosest replica for the given row in the same data center as the coodindator node is contacted to fulfill theread request. In the background a read repair is potentially initiated, based on the read_repair_chancesetting of the table, for the other replicas.

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Write requests

The coordinator sends a write request to all replicas that own the row being written. As long as all replicanodes are up and available, they will get the write regardless of the consistency level specified by theclient. The write consistency level determines how many replica nodes must respond with a successacknowledgment in order for the write to be considered successful. Success means that the data waswritten to the commit log and the memtable as described in About writes.

For example, in a single data center 10 node cluster with a replication factor of 3, an incoming write willgo to all 3 nodes that own the requested row. If the write consistency level specified by the client is ONE,the first node to complete the write responds back to the coordinator, which then proxies the successmessage back to the client. A consistency level of ONE means that it is possible that 2 of the 3 replicascould miss the write if they happened to be down at the time the request was made. If a replica missesa write, Cassandra will make the row consistent later using one of its built-in repair mechanisms: hintedhandoff, read repair, or anti-entropy node repair.

That node forwards the write to all replicas of that row. It responds back to the client once it receives awrite acknowledgment from the number of nodes specified by the consistency level.

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Multiple data center write requests

In multiple data center deployments, Cassandra optimizes write performance by choosing one coordinatornode. The coordinator node contacted by the client application forwards the write request to each replicanode in each all the data centers.

If using a consistency level of LOCAL_ONE or LOCAL_QUORUM, only the nodes in the same data centeras the coordinator node must respond to the client request in order for the request to succeed. This way,geographical latency does not impact client request response times.

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Configuration

The cassandra.yaml configuration fileThe cassandra.yaml file is the main configuration file for Cassandra.

Important: After changing properties in the cassandra.yaml file, you must restart the node forthe changes to take effect. It is located in the following directories:

• Cassandra Package installations: /etc/cassandra/conf• Cassandra Tarball installations: install_location/conf• DataStax Enterprise Package installations: /etc/dse/cassandra• DataStax Enterprise Tarball installations: install_location/resources/cassandra/conf

The configuration properties are grouped into the following sections:

• Quick start

The minimal properties needed for configuring a cluster.• Commonly used

Properties most frequently used when configuring Cassandra.• Performance tuning

Tuning performance and system resource utilization, including commit log, compaction, memory, disk I/O, CPU, reads, and writes.

• Advanced

Properties for advanced users or properties that are less commonly used.• Security

Server and client security settings.

Note: Values with note indicate default values that are defined internally, missing, commented out,or implementation depends on other properties in the cassandra.yaml file. Additionally, somecommented out values may not match the actual default value; these values are recommendedwhen changing from the default.

Quick start properties

The minimal properties needed for configuring a cluster.

Related information: Initializing a multiple node cluster (single data center) and Initializing a multiple nodecluster (multiple data centers).

cluster_name

(Default: Test Cluster) The name of the cluster. This setting prevents nodes in one logical cluster from joininganother. All nodes in a cluster must have the same value.

listen_address

(Default: localhost) The IP address or hostname that Cassandra binds to for connecting to other Cassandranodes. Set this parameter or listen_interface, not both. You must change the default setting for multiplenodes to communicate:

• Generally set to empty. If the node is properly configured (host name, name resolution, and so on),Cassandra uses InetAddress.getLocalHost() to get the local address from the system.

• For a single node cluster, you can use the default setting (localhost).• If Cassandra can't find the correct address, you must specify the IP address or host name.

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• Never specify 0.0.0.0; it is always wrong.

listen_interface

(Default: eth0)note The interface that Cassandra binds to for connecting to other Cassandra nodes. Interfacesmust correspond to a single address, IP aliasing is not supported. See listen_address.

Default directories

If you have changed any of the default directories during installation, make sure you have root access andset these properties:

commitlog_directory

The directory where the commit log is stored. Default locations:

• Package installations: /var/lib/cassandra/commitlog• Tarball installations: install_location/data/commitlog

For optimal write performance, place the commit log be on a separate disk partition, or (ideally) a separatephysical device from the data file directories. Because the commit log is append only, an HDD for isacceptable for this purpose.

data_file_directories

The directory location where table data (SSTables) is stored. Cassandra distributes data evenly across thelocation, subject to the granularity of the configured compaction strategy. Default locations:

• Package installations: /var/lib/cassandra/data• Tarball installations: install_location/data/data

As a production best practice, use RAID 0 and SSDs.

saved_caches_directory

The directory location where table key and row caches are stored. Default location:

• Package installations: /var/lib/cassandra/saved_caches• Tarball installations: install_location/data/saved_caches

Commonly used properties

Properties most frequently used when configuring Cassandra.

Before starting a node for the first time, you should carefully evaluate your requirements.

Common initialization properties

Note: Be sure to set the properties in the Quick start section as well.

commit_failure_policy

(Default: stop) Policy for commit disk failures:

• die

Shut down gossip and Thrift and kill the JVM, so the node can be replaced.• stop

Shut down gossip and Thrift, leaving the node effectively dead, but can be inspected using JMX.• stop_commit

Shut down the commit log, letting writes collect but continuing to service reads (as in pre-2.0.5Cassandra).

• ignore

Ignore fatal errors and let the batches fail.

disk_failure_policy

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(Default: stop) Sets how Cassandra responds to disk failure. Recommend settings are stop or best_effort.

• die

Shut down gossip and Thrift and kill the JVM for any file system errors or single SSTable errors, so thenode can be replaced.

• stop_paranoid

Shut down gossip and Thrift even for single SSTable errors.• stop

Shut down gossip and Thrift, leaving the node effectively dead, but available for inspection using JMX.• best_effort

Stop using the failed disk and respond to requests based on the remaining available SSTables. Thismeans you will see obsolete data at consistency level of ONE.

• ignore

Ignores fatal errors and lets the requests fail; all file system errors are logged but otherwise ignored.Cassandra acts as in versions prior to 1.2.

Related information: Handling Disk Failures In Cassandra 1.2 blog

endpoint_snitch

(Default: org.apache.cassandra.locator.SimpleSnitch) Set to a class that implements theIEndpointSnitch. Cassandra uses snitches for locating nodes and routing requests.

• SimpleSnitch

Use for single-data center deployments or single-zone in public clouds. Does not recognize data centeror rack information. It treats strategy order as proximity, which can improve cache locality when disablingread repair.

• GossipingPropertyFileSnitch

Recommended for production. The rack and data center for the local node are defined in thecassandra-rackdc.properties file and propagated to other nodes via gossip. To allow migrationfrom the PropertyFileSnitch, it uses the cassandra-topology.properties file if it is present.

• PropertyFileSnitch

Determines proximity by rack and data center, which are explicitly configured in the cassandra-topology.properties file.

• Ec2Snitch

For EC2 deployments in a single region. Loads region and availability zone information from the EC2API. The region is treated as the data center and the availability zone as the rack. Uses only private IPs.Subsequently it does not work across multiple regions.

• Ec2MultiRegionSnitch

Uses public IPs as the broadcast_address to allow cross-region connectivity. This means you must alsoset seed addresses to the public IP and open the storage_port or ssl_storage_port on the public IPfirewall. For intra-region traffic, Cassandra switches to the private IP after establishing a connection.

• RackInferringSnitch:

Proximity is determined by rack and data center, which are assumed to correspond to the 3rd and 2ndoctet of each node's IP address, respectively. This snitch is best used as an example for writing a customsnitch class (unless this happens to match your deployment conventions).

Related information: Snitches

rpc_address

(Default: localhost) The listen address for client connections (Thrift RPC service and native transport).Validvalues are:

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• unset:

Resolves the address using the hostname configuration of the node. If left unset, the hostname mustresolve to the IP address of this node using /etc/hostname, /etc/hosts, or DNS.

• 0.0.0.0:

Listens on all configured interfaces, but you must set the broadcast_rpc_address to a value other than0.0.0.0.

• IP address• hostname

Related information: Network

rpc_interface

(Default: eth1)note The listen address for client connections. Interfaces must correspond to a single address,IP aliasing is not supported. See rpc_address.

seed_provider

The addresses of hosts deemed contact points. Cassandra nodes use the -seeds list to find each other andlearn the topology of the ring.

• class_name (Default: org.apache.cassandra.locator.SimpleSeedProvider)

The class within Cassandra that handles the seed logic. It can be customized, but this is typically notrequired.

• - seeds (Default: 127.0.0.1)

A comma-delimited list of IP addresses used by gossip for bootstrapping new nodes joining a cluster.When running multiple nodes, you must change the list from the default value. In multiple data-centerclusters, the seed list should include at least one node from each data center (replication group). Morethan a single seed node per data center is recommended for fault tolerance. Otherwise, gossip has tocommunicate with another data center when bootstrapping a node. Making every node a seed node isnot recommended because of increased maintenance and reduced performance.


Common compaction settings

compaction_throughput_mb_per_sec

(Default: 16) Throttles compaction to the specified total throughput across the entire system. The faster youinsert data, the faster you need to compact in order to keep the SSTable count down. The recommendedvalue is 16 to 32 times the rate of write throughput (in MB/second). Setting the value to 0 disables compactionthrottling.

Related information: Configuring compaction

Common memtable settings

memtable_total_space_in_mb

(Default: 1/4 of heap)note Specifies the total memory used for all memtables on a node. This replaces theper-table storage settings memtable_operations_in_millions and memtable_throughput_in_mb.

Related information: Tuning the Java heap

Common disk settings

concurrent_reads

(Default: 32)note For workloads with more data than can fit in memory, the bottleneck is reads fetching datafrom disk. Setting to (16 × number_of_drives) allows operations to queue low enough in the stack so thatthe OS and drives can reorder them.

concurrent_writes

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(Default: 32)note Writes in Cassandra are rarely I/O bound, so the ideal number of concurrent writes dependson the number of CPU cores in your system. The recommended value is 8 × number_of_cpu_cores.

concurrent_counter_writes

(Default: 32)note Counter writes read the current values before incrementing and writing them back. Therecommended value is (16 × number_of_drives) .

Common automatic backup settings

incremental_backups

(Default: false) Backs up data updated since the last snapshot was taken. When enabled, Cassandra createsa hard link to each SSTable flushed or streamed locally in a backups/ subdirectory of the keyspace data.Removing these links is the operator's responsibility.

Related information: Enabling incremental backups

snapshot_before_compaction

(Default: false) Enable or disable taking a snapshot before each compaction. This option is useful to backup data when there is a data format change. Be careful using this option because Cassandra does not cleanup older snapshots automatically.


Common fault detection setting

phi_convict_threshold

(Default: 8)note Adjusts the sensitivity of the failure detector on an exponential scale. Generally this settingnever needs adjusting.

Related information: Failure detection and recovery

Performance tuning properties

Tuning performance and system resource utilization, including commit log, compaction, memory, disk I/O,CPU, reads, and writes.

Commit log settings

commitlog_sync

(Default: periodic) The method that Cassandra uses to acknowledge writes in milliseconds:

• periodic: (Default: 10000 milliseconds [10 seconds])

Used with commitlog_sync_period_in_ms to control how often the commit log is synchronized to disk.Periodic syncs are acknowledged immediately.

• batch: (Default: disabled)note

Used with commitlog_sync_batch_window_in_ms to control how long Cassandra waits for other writesbefore performing a sync. When using this method, writes are not acknowledged until fsynced to disk.

Related information: Durability

commitlog_periodic_queue_size

(Default: 1024 × number_of_cpu_cores) pending entries on the commitlog queue). When writing very largeblobs, reduce this number. For example, 16 × number_of_cpu_cores works reasonably well for 1MB blobs.This setting should be at least as large as the concurrent_writes setting.

commitlog_segment_size_in_mb

(Default: 32MB) Sets the size of the individual commitlog file segments. A commitlog segment may bearchived, deleted, or recycled after all its data has been flushed to SSTables. This amount of data canpotentially include commitlog segments from every table in the system. The default size is usually suitablefor most commitlog archiving, but if you want a finer granularity, 8 or 16 MB is reasonable.

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Related information: Commit log archive configuration

commitlog_total_space_in_mb

(Default: 32MB for 32-bit JVMs, 8192MB for 64-bit JVMs)note Total space used for commitlogs. If the usedspace goes above this value, Cassandra rounds up to the next nearest segment multiple and flushesmemtables to disk for the oldest commitlog segments, removing those log segments. This reduces theamount of data to replay on start-up, and prevents infrequently-updated tables from indefinitely keepingcommitlog segments. A small total commitlog space tends to cause more flush activity on less-active tables.

Related information: Configuring memtable throughput

Compaction settings


compaction_preheat_key_cache

(Default: true) When set to true, cached row keys are tracked during compaction, and re-cached to theirnew positions in the compacted SSTable. If you have extremely large key caches for tables, set the valueto false; see Global row and key caches properties.

concurrent_compactors

(Default: Smaller of number of disks or number of cores, with a minimum of 2 and a maximum of 8per CPU core)note Sets the number of concurrent compaction processes allowed to run simultaneouslyon a node, not including validation compactions for anti-entropy repair. Simultaneous compactionshelp preserve read performance in a mixed read-write workload by mitigating the tendency of smallSSTables to accumulate during a single long-running compaction. If your data directories are backed bySSD, increase this value to the number of cores. If compaction running too slowly or too fast, adjustcompaction_throughput_mb_per_sec first.

in_memory_compaction_limit_in_mb

(Default: 64MB) Size limit for rows being compacted in memory. Larger rows spill to disk and use aslower two-pass compaction process. When this occurs, a message is logged specifying the row key. Therecommended value is 5 to 10 percent of the available Java heap size.

preheat_kernel_page_cache

(Default: false) Enable or disable kernel page cache preheating from contents of the key cache aftercompaction. When enabled it preheats only first page (4KB) of each row to optimize for sequential access.It can be harmful for fat rows, see CASSANDRA-4937 for more details.

sstable_preemptive_open_interval_in_mb

(Default: 50MB) When compacting, the replacement opens SSTables before they are completely writtenand uses in place of the prior SSTables for any range previously written. This setting helps to smoothlytransfer reads between the SSTables by reducing page cache churn and keeps hot rows hot.

Memtable settings

memtable_allocation_type

(Default: heap_buffers) Specify the way Cassandra allocates and manages memtable memory. See Off-heap memtables in Cassandra 2.1. Options are:

• heap_buffers

On heap NIO (non-blocking I/O) buffers.• offheap_buffers

Off heap (direct) NIO buffers.• offheap_objects

Native memory, eliminating NIO buffer heap overhead.

memtable_cleanup_threshold

(Default: 0.11 1/(memtable_flush_writers + 1))note Ratio of occupied non-flushing memtable size to totalpermitted size for triggering a flush of the largest memtable. Larger values mean larger flushes and less

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compaction, but also less concurrent flush activity, which can make it difficult to keep your disks saturatedunder heavy write load.

file_cache_size_in_mb

(Default: Smaller of 1/4 heap or 512) Total memory to use for SSTable-reading buffers.

memtable_flush_queue_size

(Default: 4) The number of full memtables to allow pending flush (memtables waiting for a write thread). Ata minimum, set to the maximum number of indexes created on a single table.

Related information: Flushing data from the memtable

memtable_flush_writers

(Default: Smaller of number of disks or number of cores with a minimum of 2 and a maximum of 8)note Setsthe number of memtable flush writer threads. These threads are blocked by disk I/O, and each one holdsa memtable in memory while blocked. If your data directories are backed by SSD, increase this setting tothe number of cores.

memtable_heap_space_in_mb

(Default: 1/4 heap)note Total permitted memory to use for memtables. Triggers a flush based onmemtable_cleanup_threshold. Cassandra stops accepting writes when the limit is exceeded until a flushcompletes. If unset, sets to default.

memtable_offheap_space_in_mb

(Default: 1/4 heap)note See memtable_heap_space_in_mb.

Cache and index settings

column_index_size_in_kb

(Default: 64) Granularity of the index of rows within a partition. For huge rows, decrease this setting toimprove seek time. If you use key cache, be careful not to make this setting too large because key cachewill be overwhelmed. If you're unsure of the size of the rows, it's best to use the default setting.

index_summary_capacity_in_mb

(Default: 5% of the heap size [empty])note Fixed memory pool size in MB for SSTable index summaries. Ifthe memory usage of all index summaries exceeds this limit, any SSTables with low read rates shrink theirindex summaries to meet this limit. This is a best-effort process. In extreme conditions, Cassandra mayneed to use more than this amount of memory.

index_summary_resize_interval_in_minutes

(Default: 60 minutes) How frequently index summaries should be re-sampled. This is done periodically toredistribute memory from the fixed-size pool to SSTables proportional their recent read rates. To disable,set to -1. This leaves existing index summaries at their current sampling level.

reduce_cache_capacity_to

(Default: 0.6) Sets the size percentage to which maximum cache capacity is reduced when Java heap usagereaches the threshold defined by reduce_cache_sizes_at.

reduce_cache_sizes_at

(Default: 0.85) When Java heap usage (after a full concurrent mark sweep (CMS) garbage collection)exceeds this percentage, Cassandra reduces the cache capacity to the fraction of the current size asspecified by reduce_cache_capacity_to. To disable, set the value to 1.0.

Disks settings

stream_throughput_outbound_megabits_per_sec

(Default: 200 seconds)note Throttles all outbound streaming file transfers on a node to the specifiedthroughput. Cassandra does mostly sequential I/O when streaming data during bootstrap or repair, whichcan lead to saturating the network connection and degrading client (RPC) performance.

inter_dc_stream_throughput_outbound_megabits_per_sec

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(Default: unset)note Throttles all streaming file transfer between the data centers. This setting allows throttlesstreaming throughput betweens data centers in addition to throttling all network stream traffic as configuredwith stream_throughput_outbound_megabits_per_sec.

trickle_fsync

(Default: false) When doing sequential writing, enabling this option tells fsync to force the operating systemto flush the dirty buffers at a set interval trickle_fsync_interval_in_kb. Enable this parameter to avoid suddendirty buffer flushing from impacting read latencies. Recommended to use on SSDs, but not on HDDs.

trickle_fsync_interval_in_kb

(Default: 10240). Sets the size of the fsync in kilobytes.

Advanced properties

Properties for advanced users or properties that are less commonly used.

Advanced initialization properties

auto_bootstrap

(Default: true) This setting has been removed from default configuration. It makes new (non-seed) nodesautomatically migrate the right data to themselves. When initializing a fresh cluster without data, addauto_bootstrap: false.


batch_size_warn_threshold_in_kb

(Default: 5KB per batch) Log WARN on any batch size exceeding this value in kilobytes. Caution should betaken on increasing the size of this threshold as it can lead to node instability.

broadcast_address

(Default: listen_address)note The IP address a node tells other nodes in the cluster to contact it by. It allowspublic and private address to be different. For example, use the broadcast_address parameter in topologieswhere not all nodes have access to other nodes by their private IP addresses.

If your Cassandra cluster is deployed across multiple Amazon EC2 regions and you use theEC2MultiRegionSnitch, set the broadcast_address to public IP address of the node and thelisten_address to the private IP.

initial_token

(Default: disabled) Used in the single-node-per-token architecture, where a node owns exactly onecontiguous range in the ring space. Setting this property overrides num_tokens.

If you not using vnodes or have num_tokens set it to 1 or unspecified (#num_tokens), you should alwaysspecify this parameter when setting up a production cluster for the first time and when adding capacity. Formore information, see this parameter in the Cassandra 1.1 Node and Cluster Configuration documentation.

This parameter can be used with num_tokens (vnodes ) in special cases such as Restoring from a Snapshot.

num_tokens

(Default: 256) note Defines the number of tokens randomly assigned to this node on the ring when usingvirtual nodes (vnodes). The more tokens, relative to other nodes, the larger the proportion of data thatthe node stores. Generally all nodes should have the same number of tokens assuming equal hardwarecapability. The recommended value is 256. If unspecified (#num_tokens), Cassandra uses 1 (equivalentto #num_tokens : 1) for legacy compatibility and uses the initial_token setting.

If not using vnodes, comment #num_tokens : 256 or set num_tokens : 1 and use initial_token. Ifyou already have an existing cluster with one token per node and wish to migrate to vnodes, see Enablingvirtual nodes on an existing production cluster.

Note: If using DataStax Enterprise, the default setting of this property depends on the type of nodeand type of install.

http://www.datastax.com/docs/1.1/configuration/node_configuration#initial-token

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partitioner

(Default: org.apache.cassandra.dht.Murmur3Partitioner) Distributes rows (by partition key)across all nodes in the cluster. Any IPartitioner may be used, including your own as long as it is in theclass path. For new clusters use the default partitioner.

Cassandra provides the following partitioners for backwards compatibility:

• RandomPartitioner

• ByteOrderedPartitioner

• OrderPreservingPartitioner (deprecated)

Related information: Partitioners

storage_port

(Default: 7000) The port for inter-node communication.

Advanced automatic backup setting

auto_snapshot

(Default: true) Enable or disable whether a snapshot is taken of the data before keyspace truncation ordropping of tables. To prevent data loss, using the default setting is strongly advised. If you set to false,you will lose data on truncation or drop.

Key caches and global row properties

When creating or modifying tables, you enable or disable the key cache (partition key cache) or row cachefor that table by setting the caching parameter. Other row and key cache tuning and configuration optionsare set at the global (node) level. Cassandra uses these settings to automatically distribute memory foreach table on the node based on the overall workload and specific table usage. You can also configure thesave periods for these caches globally.

Related information: Configuring caches

key_cache_keys_to_save

(Default: disabled - all keys are saved)note Number of keys from the key cache to save.

key_cache_save_period

(Default: 14400 seconds [4 hours]) Duration in seconds that keys are saved in cache. Caches are savedto saved_caches_directory. Saved caches greatly improve cold-start speeds and has relatively little effecton I/O.

key_cache_size_in_mb

(Default: empty) A global cache setting for tables. It is the maximum size of the key cache in memory. Whenno value is set, the cache is set to the smaller of 5% of the available heap, or 100MB. To disable set to 0.

Related information: setcachecapacity.

row_cache_keys_to_save

(Default: disabled - all keys are saved)note Number of keys from the row cache to save.

row_cache_size_in_mb

(Default: 0- disabled) Maximum size of the row cache in memory. Row cache can save more time thankey_cache_size_in_mb, but is space-intensive because it contains the entire row. Use the row cache onlyfor hot rows or static rows. If you reduce the size, you may not get you hottest keys loaded on start up.

row_cache_save_period

(Default: 0- disabled) Duration in seconds that rows are saved in cache. Caches are saved tosaved_caches_directory. This setting has limited use as described in row_cache_size_in_mb.

memory_allocator

(Default: NativeAllocator) The off-heap memory allocator. In addition to caches, this property affects storageengine meta data. Supported values:

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• NativeAllocator• JEMallocAllocator

Experiments show that jemalloc saves some memory compared to the native allocator because it ismore fragmentation resistant. To use, install jemalloc as a library and modify cassandra-env.sh(instructions in file).

Counter caches properties

Counter cache helps to reduce counter locks' contention for hot counter cells. In case of RF = 1 a countercache hit will cause Cassandra to skip the read before write entirely. With RF > 1 a counter cache hit willstill help to reduce the duration of the lock hold, helping with hot counter cell updates, but will not allowskipping the read entirely. Only the local (clock, count) tuple of a counter cell is kept in memory, not thewhole counter, so it's relatively cheap.

Note: Reducing the size counter cache may result in not getting the hottest keys loaded on start-up.

counter_cache_size_in_mb

(Default value: empty)note When no value is specified a minimum of 2.5% of Heap or 50MB. If you performcounter deletes and rely on low gc_grace_seconds, you should disable the counter cache. To disable, setto 0.

counter_cache_save_period

(Default: 7200 seconds [2 hours]) Duration after which Cassandra should save the counter cache (keysonly). Caches are saved to saved_caches_directory.

counter_cache_keys_to_save

(Default value: disabled)note Number of keys from the counter cache to save. When disabled all keys aresaved.

Tombstone settings

When executing a scan, within or across a partition, tombstones must be kept in memory to allow returningthem to the coordinator. The coordinator uses them to ensure other replicas know about the deleted rows.Workloads that generate numerous tombstones may cause performance problems and exhaust the serverheap. See Cassandra anti-patterns: Queues and queue-like datasets. Adjust these thresholds only if youunderstand the impact and want to scan more tombstones. Additionally, you can adjust these thresholds atruntime using the StorageServiceMBean.

Related information: Cassandra anti-patterns: Queues and queue-like datasets

tombstone_warn_threshold

(Default: 1000) The maximum number of tombstones a query can scan before warning.

tombstone_failure_threshold

(Default: 100000) The maximum number of tombstones a query can scan before aborting.

Network timeout settings

range_request_timeout_in_ms

(Default: 10000 milliseconds) The time that the coordinator waits for sequential or index scans to complete.

read_request_timeout_in_ms

(Default: 5000 milliseconds) The time that the coordinator waits for read operations to complete.

counter_write_request_timeout_in_ms

(Default: 5000 milliseconds) The time that the coordinator waits for counter writes to complete.

cas_contention_timeout_in_ms

(Default: 1000 milliseconds) The time that the coordinator continues to retry a CAS (compare and set)operation that contends with other proposals for the same row.

truncate_request_timeout_in_ms

/documentation/cql/3.1/cql/cql_reference/tabProp.html?scroll=tabProp__tabProp_gc_grace

http://www.datastax.com/dev/blog/cassandra-anti-patterns-queues-and-queue-like-datasets

http://www.datastax.com/dev/blog/cassandra-anti-patterns-queues-and-queue-like-datasets

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(Default: 60000 milliseconds) The time that the coordinator waits for truncates (remove all data from atable) to complete. The long default value allows for a snapshot to be taken before removing the data. Ifauto_snapshot is disabled (not recommended), you can reduce this time.

write_request_timeout_in_ms

(Default: 2000 milliseconds) The time that the coordinator waits for write operations to complete.

Related information: About hinted handoff writes

request_timeout_in_ms

(Default: 10000 milliseconds) The default time for other, miscellaneous operations.


Inter-node settings

cross_node_timeout

(Default: false) Enable or disable operation timeout information exchange between nodes (to accuratelymeasure request timeouts). If disabled Cassandra assumes the request are forwarded to the replica instantlyby the coordinator, which means that under overload conditions extra time is required for processing already-timed-out requests..

Caution: Before enabling this property make sure NTP (network time protocol) is installed and thetimes are synchronized between the nodes.

internode_send_buff_size_in_bytes

(Default: N/A)note Sets the sending socket buffer size in bytes for inter-node calls.

When setting this parameter and internode_recv_buff_size_in_bytes, the buffer size is limited bynet.core.wmem_max. When unset, buffer size is defined by net.ipv4.tcp_wmem. See man tcp and:

• /proc/sys/net/core/wmem_max

• /proc/sys/net/core/rmem_max

• proc/sys/net/ipv4/tcp_wmem

• /proc/sys/net/ipv4/tcp_wmem

internode_recv_buff_size_in_bytes

(Default: N/A)note Sets the receiving socket buffer size in bytes for inter-node calls.

internode_compression

(Default: all) Controls whether traffic between nodes is compressed. The valid values are:

• all

All traffic is compressed.• dc

Traffic between data centers is compressed.• none

No compression.

inter_dc_tcp_nodelay

(Default: false) Enable or disable tcp_nodelay for inter-data center communication. When disabled larger,but fewer, network packets are sent. This reduces overhead from the TCP protocol itself. However, if crossdata-center responses are blocked, it will increase latency.

streaming_socket_timeout_in_ms

(Default: 0 - never timeout streams)note Enable or disable socket timeout for streaming operations. Whena timeout occurs during streaming, streaming is retried from the start of the current file. Avoid setting thisvalue too low, as it can result in a significant amount of data re-streaming.

Native transport (CQL Binary Protocol)

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start_native_transport

(Default: true) Enable or disable the native transport server. Uses the same address as the rpc_address,but the port is different from the rpc_port. See native_transport_port.

native_transport_port

(Default: 9042) Port on which the CQL native transport listens for clients.

native_transport_max_threads

(Default: 128)note The maximum number of thread handling requests. Similar to rpc_max_threads and differsas follows:

• Default is different (128 versus unlimited).• No corresponding native_transport_min_threads.• Idle threads are stopped after 30 seconds.

native_transport_max_frame_size_in_mb

(Default: 256MB) The maximum size of allowed frame. Frame (requests) larger than this are rejected asinvalid.

RPC (remote procedure call) settings

Settings for configuring and tuning client connections.

broadcast_rpc_address

(Default: unset)note RPC address to broadcast to drivers and other Cassandra nodes. This cannot be set to0.0.0.0. If blank, it is set to the value of the rpc_address or rpc_interface. If rpc_address or rpc_interfaceisset to 0.0.0.0, this property must be set.

rpc_port

(Default: 9160) Thrift port for client connections.

start_rpc

(Default: true) Starts the Thrift RPC server.

rpc_keepalive

(Default: true) Enable or disable keepalive on client connections (RPC or native).

rpc_max_threads

(Default: unlimited)note Regardless of your choice of RPC server (rpc_server_type), the number of maximumrequests in the RPC thread pool dictates how many concurrent requests are possible. However, if you areusing the parameter sync in the rpc_server_type, it also dictates the number of clients that can be connected.For a large number of client connections, this could cause excessive memory usage for the thread stack.Connection pooling on the client side is highly recommended. Setting a maximum thread pool size acts as asafeguard against misbehaved clients. If the maximum is reached, Cassandra blocks additional connectionsuntil a client disconnects.

rpc_min_threads

(Default: 16)note Sets the minimum thread pool size for remote procedure calls.

rpc_recv_buff_size_in_bytes

(Default: N/A)note Sets the receiving socket buffer size for remote procedure calls.

rpc_send_buff_size_in_bytes

(Default: N/A)note Sets the sending socket buffer size in bytes for remote procedure calls.

rpc_server_type

(Default: sync) Cassandra provides three options for the RPC server. On Windows, sync is about 30%slower than hsha. On Linux, sync and hsha performance is about the same, but hsha uses less memory.

• sync: (Default One thread per Thrift connection.)

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For a very large number of clients, memory is the limiting factor. On a 64-bit JVM, 180KB is the minimumstack size per thread and corresponds to your use of virtual memory. Physical memory may be limiteddepending on use of stack space.

• hsha:

Half synchronous, half asynchronous. All Thrift clients are handled asynchronously using a small numberof threads that does not vary with the number of clients and thus scales well to many clients. The RPCrequests are synchronous (one thread per active request).

Note: When selecting this option, you must change the default value (unlimited) ofrpc_max_threads.

• Your own RPC server

You must provide a fully-qualified class name of an o.a.c.t.TServerFactory that can create aserver instance.

Advanced fault detection settings

Settings to handle poorly performing or failing nodes.

dynamic_snitch_badness_threshold

(Default: 0.1) Sets the performance threshold for dynamically routing client requests away from a poorlyperforming node. Specifically, it controls how much worse a poorly performing node has to be before thedynamic snitch prefers other replicas over it. A value of 0.2 means Cassandra continues to prefer the staticsnitch values until the node response time is 20% worse than the best performing node. Until the thresholdis reached, incoming requests are statically routed to the closest replica (as determined by the snitch). Ifthe value of this parameter is greater than zero and read_repair_chance is less than 1.0, cache capacityis maximized across the nodes.

dynamic_snitch_reset_interval_in_ms

(Default: 600000 milliseconds) Time interval to reset all node scores, which allows a bad node to recover.

dynamic_snitch_update_interval_in_ms

(Default: 100 milliseconds) The time interval for how often the snitch calculates node scores. Because scorecalculation is CPU intensive, be careful when reducing this interval.

hinted_handoff_enabled

(Default: true) Enable or disable hinted handoff. To enable per data center, add data center list. Forexample: hinted_handoff_enabled: DC1,DC2. A hint indicates that the write needs to be replayed toan unavailable node. Where Cassandra writes the hint depends on the version:

• Prior to 1.0

Writes to a live replica node.• 1.0 and later

Writes to the coordinator node.


hinted_handoff_throttle_in_kb

(Default: 1024) Maximum throttle per delivery thread in kilobytes per second. This rate reduces proportionallyto the number of nodes in the cluster. For example, if there are two nodes in the cluster, each delivery threadwill use the maximum rate. If there are three, each node will throttle to half of the maximum, since the twonodes are expected to deliver hints simultaneously.

max_hint_window_in_ms

(Default: 10800000 milliseconds [3 hours]) Maximum amount of time that hints are generates hints for anunresponsive node. After this interval, new hints are no longer generated until the node is back up andresponsive. If the node goes down again, a new interval begins. This setting can prevent a sudden demandfor resources when a node is brought back online and the rest of the cluster attempts to replay a largevolume of hinted writes.


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Related information: Failure detection and recovery

max_hints_delivery_threads

(Default: 2) Number of threads with which to deliver hints. In multiple data-center deployments, considerincreasing this number because cross data-center handoff is generally slower.

batchlog_replay_throttle_in_kb

(Default: 1024KB per second) Total maximum throttle. Throttling is reduced proportionally to the numberof nodes in the cluster.

Request scheduler properties

Settings to handle incoming client requests according to a defined policy. If you need to use theseproperties, your nodes are overloaded and dropping requests. It is recommended that you add more nodesand not try to prioritize requests.

request_scheduler

(Default: org.apache.cassandra.scheduler.NoScheduler) Defines a scheduler to handle incomingclient requests according to a defined policy. This scheduler is useful for throttling client requests in singleclusters containing multiple keyspaces. This parameter is specifically for requests from the client and doesnot affect inter-node communication. Valid values are:

• org.apache.cassandra.scheduler.NoScheduler

No scheduling takes place.• org.apache.cassandra.scheduler.RoundRobinScheduler

Round robin of client requests to a node with a separate queue for each request_scheduler_id property.• A Java class that implements the RequestScheduler interface.

request_scheduler_id

(Default: keyspace)note An identifier on which to perform request scheduling. Currently the only valid valueis keyspace. See weights.

request_scheduler_options

(Default: disabled) Contains a list of properties that define configuration options for request_scheduler:

• throttle_limit

The number of in-flight requests per client. Requests beyond this limit are queued up until runningrequests complete. Recommended value is ((concurrent_reads + concurrent_writes) × 2).

• default_weight: (Default: 1)note

How many requests are handled during each turn of the RoundRobin.• weights: (Default: Keyspace: 1)

Takes a list of keyspaces. It sets how many requests are handled during each turn of the RoundRobin,based on the request_scheduler_id.

Thrift interface properties

Legacy API for older clients. CQL is a simpler and better API for Cassandra.

thrift_framed_transport_size_in_mb

(Default: 15) Frame size (maximum field length) for Thrift. The frame is the row or part of the row that theapplication is inserting.

thrift_max_message_length_in_mb

(Default: 16) The maximum length of a Thrift message in megabytes, including all fields and internal Thriftoverhead (1 byte of overhead for each frame). Message length is usually used in conjunction with batches.A frame length greater than or equal to 24 accommodates a batch with four inserts, each of which is 24bytes. The required message length is greater than or equal to 24+24+24+24+4 (number of frames).


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Security properties

Server and client security settings.

authenticator

(Default: AllowAllAuthenticator) The authentication backend. It implements IAuthenticator foridentifying users. The available authenticators are:

• AllowAllAuthenticator:

Disables authentication; no checks are performed.• PasswordAuthenticator

Authenticates users with user names and hashed passwords stored in the system_auth.credentials table.If you use the default, 1, and the node with the lone replica goes down, you will not be able to log intothe cluster because the system_auth keyspace was not replicated.

Related information: Internal authentication

internode_authenticator

(Default: enabled)note Internode authentication backend. It implementsorg.apache.cassandra.auth.AllowAllInternodeAuthenticator to allows or disallowconnections from peer nodes.

authorizer

(Default: AllowAllAuthorizer) The authorization backend. It implements IAuthenticator to limit accessand provide permissions. The available authorizers are:

• AllowAllAuthorizer

Disables authorization; allows any action to any user.• CassandraAuthorizer

Stores permissions in system_auth.permissions table. If you use the default, 1, and the node with thelone replica goes down, you will not be able to log into the cluster because the system_auth keyspacewas not replicated.

Related information: Object permissions

permissions_validity_in_ms

(Default: 2000) How long permissions in cache remain valid. Depending on the authorizer, such asCassandraAuthorizer, fetching permissions can be resource intensive. This setting disabled when setto 0 or when AllowAllAuthorizer is set.

Related information: Object permissions

server_encryption_options

Enable or disable inter-node encryption. You must also generate keys and provide the appropriate key andtrust store locations and passwords. No custom encryption options are currently enabled. The availableoptions are:

• internode_encryption: (Default: none) Enable or disable encryption of inter-node communicationusing the TLS_RSA_WITH_AES_128_CBC_SHA cipher suite for authentication, key exchange, andencryption of data transfers. Use the DHE/ECDHE ciphers if running in (Federal Information ProcessingStandard) FIPS 140 compliant mode. The available inter-node options are:

• all

Encrypt all inter-node communications.• none

No encryption.• dc

Encrypt the traffic between the data centers (server only).

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• rack

Encrypt the traffic between the racks (server only).• keystore: (Default: conf/.keystore)

The location of a Java keystore (JKS) suitable for use with Java Secure Socket Extension (JSSE), whichis the Java version of the Secure Sockets Layer (SSL), and Transport Layer Security (TLS) protocols.The keystore contains the private key used to encrypt outgoing messages.

• keystore_password: (Default: cassandra)

Password for the keystore.• truststore: (Default: conf/.truststore)

Location of the truststore containing the trusted certificate for authenticating remote servers.• truststore_password: (Default: cassandra)

Password for the truststore.

The passwords used in these options must match the passwords used when generating the keystore andtruststore. For instructions on generating these files, see Creating a Keystore to Use with JSSE.

The advanced settings are:

• protocol: (Default: TLS)• algorithm: (Default: SunX509)• store_type: (Default: JKS)• cipher_suites: (Default:

TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_256_CBC_SHA)• require_client_auth: (Default: false)

Enables or disables certificate authentication.

Related information: Node-to-node encryption

client_encryption_options

Enable or disable client-to-node encryption. You must also generate keys and provide the appropriate keyand trust store locations and passwords. No custom encryption options are currently enabled. The availableoptions are:

• enabled: (Default: false)

To enable, set to true.• keystore: (Default: conf/.keystore)

The location of a Java keystore (JKS) suitable for use with Java Secure Socket Extension (JSSE), whichis the Java version of the Secure Sockets Layer (SSL), and Transport Layer Security (TLS) protocols.The keystore contains the private key used to encrypt outgoing messages.

• keystore_password: (Default: cassandra)

Password for the keystore. This must match the password used when generating the keystore andtruststore.

• require_client_auth: (Default: false)

Enables or disables certificate authentication. (Available starting with Cassandra 1.2.3.)• truststore: (Default: conf/.truststore)

Set if require_client_auth is true.• truststore_password: <truststore_password>

Set if require_client_auth is true.

The advanced settings are:

• protocol: (Default: TLS)

http://docs.oracle.com/javase/7/docs/technotes/guides/security/jsse/JSSERefGuide.html#CreateKeystore

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• algorithm: (Default: SunX509)• store_type: (Default: JKS)• cipher_suites: (Default:

TLS_RSA_WITH_AES_128_CBC_SHA,TLS_RSA_WITH_AES_256_CBC_SHA)

Related information: Client-to-node encryption

ssl_storage_port

(Default: 7001) The SSL port for encrypted communication. Unused unless enabled in encryption_options.

Configuring gossip settings

About this task

When a node first starts up, it looks at its cassandra.yaml configuration file to determine the name of theCassandra cluster it belongs to; which nodes (called seeds) to contact to obtain information about the othernodes in the cluster; and other parameters for determining port and range information.

Procedure

In the cassandra.yaml file, set the following parameters:

Property Description

cluster_name Name of the cluster that this node is joining. Mustbe the same for every node in the cluster.

listen_address The IP address or hostname that Cassandra bindsto for connecting to other Cassandra nodes.

(Optional) broadcast_address The IP address a node tells other nodes in thecluster to contact it by. It allows public and privateaddress to be different. For example, use thebroadcast_address parameter in topologieswhere not all nodes have access to other nodesby their private IP addresses. The default is thelisten_address.

seed_provider A -seeds list is comma-delimited list of hosts (IPaddresses) that gossip uses to learn the topologyof the ring. Every node should have the samelist of seeds. In multiple data-center clusters, theseed list should include at least one node fromeach data center (replication group). More than asingle seed node per data center is recommendedfor fault tolerance. Otherwise, gossip has tocommunicate with another data center whenbootstrapping a node. Making every node a seednode is not recommended because of increasedmaintenance and reduced performance.

storage_port The inter-node communication port (default is7000). Must be the same for every node in thecluster.

initial_token For legacy clusters. Used in the single-node-per-token architecture, where a node owns exactlyone contiguous range in the ring space.

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Property Description

num_tokens For new clusters. Defines the number of tokensrandomly assigned to this node on the ring whenusing virtual nodes (vnodes).

Configuring the heap dump directoryAnalyzing the heap dump file can help troubleshoot memory problems.

About this task

Cassandra starts Java with the option -XX:-HeapDumpOnOutOfMemoryError. Using this option triggersa heap dump in the event of an out-of-memory condition. The heap dump file consists of references toobjects that cause the heap to overflow. By default, Cassandra puts the file a subdirectory of the working,root directory when running as a service. If Cassandra does not have write permission to the root directory,the heap dump fails. If the root directory is too small to accommodate the heap dump, the server crashes.

For a heap dump to succeed and to prevent crashes, configure a heap dump directory that meets theserequirements:

• Accessible to Cassandra for writing• Large enough to accommodate a heap dump

This file is located in:

• Package installations: /etc/dse/cassandra• Tarball installations: install_location/resources/cassandra/conf

Base the size of the directory on the value of the Java -mx option.

Procedure

1. Open the cassandra-env.sh file for editing.

# set jvm HeapDumpPath with CASSANDRA_HEAPDUMP_DIR

2. Scroll down to the comment about the heap dump path:

# set jvm HeapDumpPath with CASSANDRA_HEAPDUMP_DIR

3. On the line after the comment, set the CASSANDRA_HEAPDUMP_DIR to the path you want to use:

# set jvm HeapDumpPath with CASSANDRA_HEAPDUMP_DIR CASSANDRA_HEAPDUMP_DIR =<path>

4. Save the cassandra-env.sh file and restart.

Generating tokensIf not using virtual nodes (vnodes), you still need to calculate tokens for your cluster.

The following topics in the Cassandra 1.1 documentation provide conceptual information about tokens:

• Data Distribution in the Ring• Replication Strategy

About calculating tokens for single or multiple data centers in Cassandra 1.2 and later

• Single data center deployments: calculate tokens by dividing the hash range by the number of nodes inthe cluster.

http://www.datastax.com/docs/1.1/cluster_architecture/partitioning#data-distribution-in-the-ring

http://www.datastax.com/docs/1.1/cluster_architecture/replication#replication-strategy

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• Multiple data center deployments: calculate the tokens for each data center so that the hash range isevenly divided for the nodes in each data center.

For more explanation, see be sure to read the conceptual information mentioned above.

The method used for calculating tokens depends on the type of partitioner:

Calculating tokens for the Murmur3Partitioner

Use this method for generating tokens when you are not using virtual nodes (vnodes) and using theMurmur3Partitioner (default). This partitioner uses a maximum possible range of hash values from -263 to+263-1. To calculate tokens for this partitioner:

python -c 'print [str(((2**64 / number_of_tokens) * i) - 2**63) for i in range(number_of_tokens)]'

For example, to generate tokens for 6 nodes:

python -c 'print [str(((2**64 / 6) * i) - 2**63) for i in range(6)]'

The command displays the token for each node:

[ '-9223372036854775808', '-6148914691236517206', '-3074457345618258604', '-2', '3074457345618258600', '6148914691236517202' ]

Calculating tokens for the RandomPartitioner

To calculate tokens when using the RandomPartitioner in Cassandra 1.2 clusters, use the Cassandra 1.1Token Generating Tool.

Configuring virtual nodes

Enabling virtual nodes on a new cluster

About this task

Generally when all nodes have equal hardware capability, they should have the same number of virtualnodes (vnodes). If the hardware capabilities vary among the nodes in your cluster, assign a proportionalnumber of vnodes to the larger machines. For example, you could designate your older machines to use128 vnodes and your new machines (that are twice as powerful) with 256 vnodes.

Procedure

Set the number of tokens on each node in your cluster with the num_tokens parameter in thecassandra.yaml file.

The recommended value is 256. Do not set the initial_token parameter.

Enabling virtual nodes on an existing production cluster

About this task

For production clusters, enabling virtual nodes (vnodes) has less impact on performance if you bring upa another data center configured with vnodes already enabled and let Cassandra automatic mechanismsdistribute the existing data into the new nodes.

Procedure

1. Add a new data center to the cluster.

http://www.datastax.com/docs/1.1/initialize/token_generation

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2. Once the new data center with vnodes enabled is up, switch your clients to use the new data center.

3. Run a full repair with nodetool repair.

This step ensures that after you move the client to the new data center that any previous writes areadded to the new data center and that nothing else, such as hints, is dropped when you remove the olddata center.

4. Update your schema to no longer reference the old data center.

5. Remove the old data center from the cluster.

See Decommissioning a data center.

Configuring loggingCassandra 2.1 introduces a new logging backend.

Cassandra provides logging functionality using Simple Logging Facade for Java (SLF4J) with a logbackbackend. Logs are written to the system.log file in the Cassandra logging directory. You can configurelogging programmatically or manually. Manual ways to configure logging are:

• Run the nodetool setlogginglevel command• Configure the logback-test.xml or logback.xml file installed with Cassandra• Use the JConsole tool to configure logging through JMX.

Logback looks for logback-test.xml first, and then for logback.xml. The logback.xml location fordifferent types of installations is listed in the "File locations" section. For example, on tarball and sourceinstallations, logback.xml is located in the install_location/conf directory.

The XML configuration files look something like this:

<configuration scan="true"> <jmxConfigurator /> <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender"> <file>${cassandra.logdir}/system.log</file> <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy"> <fileNamePattern>${cassandra.logdir}/system.log.%i.zip</fileNamePattern> <minIndex>1</minIndex> <maxIndex>20</maxIndex> </rollingPolicy>

<triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy"> <maxFileSize>20MB</maxFileSize> </triggeringPolicy> <encoder> <pattern>%-5level [%thread] %date{ISO8601} %F:%L - %msg%n</pattern>  </encoder> </appender> <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender"> <encoder> <pattern>%-5level %date{HH:mm:ss,SSS} %msg%n</pattern> </encoder> </appender> <root level="INFO"> <appender-ref ref="FILE" /> <appender-ref ref="STDOUT" />

http://logback.qos.ch/

http://logback.qos.ch/manual/configuration.html

/documentation/cassandra/2.1/cassandra/operations/ops_monitoring_c.html#concept_ds_pkn_drq_ck__opsMonitoringJconsole

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</root> <logger name="com.thinkaurelius.thrift" level="ERROR"/></configuration>

The appender configurations specify where to print the log and its configuration. The first appender directslogs to a file. The second appender directs logs to the console. You can change the following loggingfunctionality:

• Rolling policy

• The policy for rolling logs over to an archive• Location and name of the log file• Location and name of the archive• Minimum and maximum file size to trigger rolling

• Format of the message• The log level

Log levels

The valid values for setting the log level include ALL for logging information at all levels, TRACE throughERROR, and OFF for no logging. TRACE creates the most verbose log, and ERROR, the least.

• ALL• TRACE• DEBUG• INFO (Default)• WARN• ERROR• OFF

Note: Increasing logging levels can generate heavy logging output on a moderately traffickedcluster.

You can use the nodetool getlogginglevels command to see the current logging configuration.

$ nodetool getlogginglevelsLogger Name Log LevelROOT INFOcom.thinkaurelius.thrift ERROR

Migrating to logback from log4j

If you upgrade from a previous version of Cassandra that used log4j, you can convert log4j.properties filesto logback.xml using the logback PropertiesTranslator web-application.

Using log file rotation

The default policy rolls the system.log file after the size exceeds 20MB. Archives are compressed in zipformat. Logback names the log files system.log.1.zip, system.log.2.zip, and so on. For moreinformation, see logback documentation.

http://logback.qos.ch/translator/

http://logback.qos.ch/manual/appenders.html#FixedWindowRollingPolicy

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Commit log archive configurationCassandra provides commitlog archiving and point-in-time recovery.

About this task

You configure this feature in the commitlog_archiving.properties configuration file, which islocated in the following directories:

• Cassandra Package installations: /etc/cassandra/conf• Cassandra Tarball installations: install_location/conf• DataStax Enterprise Package installations: /etc/dse/cassandra• DataStax Enterprise Tarball installations: install_location/resources/cassandra/conf

The commands archive_command and restore_command expect only a single command witharguments. The parameters must be entered verbatim. STDOUT and STDIN or multiple commands cannotbe executed. To workaround, you can script multiple commands and add a pointer to this file. To disable acommand, leave it blank.

Procedure

• Archive a commitlog segment:

Command archive_command=

%path Fully qualified path of the segment toarchive.

Parameters

%name Name of the commit log.

Example archive_command=/bin/ln %path /backup/%name

• Restore an archived commitlog:

Command restore_command=

%from Fully qualified path of the an archivedcommitlog segment from therestore_directories.

Parameters

%t Name of live commit log directory.

Example restore_command=cp -f %from %to

• Set the restore directory location:

Command restore_directories=

Format restore_directories=restore_directory_location

• Restore mutations created up to and including the specified timestamp:

Command restore_point_in_time=

Format <timestamp> (YYYY:MM:DD HH:MM:SS)

Example restore_point_in_time=2013:12:1117:00:00

Restore stops when the first client-supplied timestamp is greater than the restore point timestamp.Because the order in which Cassandra receives mutations does not strictly follow the timestamp order,this can leave some mutations unrecovered.

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Hadoop support

Cassandra 2.1 improves support for integrating Hadoop with Cassandra:

• MapReduce• Apache Pig

You can use Cassandra 2.1 with Hadoop 2.x or 1.x with some restrictions.

• Isolate Cassandra and Hadoop nodes in separate data centers.• Before starting the data centers of Cassandra/Hadoop nodes, disable virtual nodes (vnodes).

To disable virtual nodes:

1. In the cassandra.yaml file, set num_tokens to 1.2. Uncomment the initial_token property and set it to 1 or to the value of a generated token for a multi-

node cluster.3. Start the cluster for the first time.

Do not disable or enable vnodes on an existing cluster.

Setup and configuration, described in the Apache docs, involves overlaying a Hadoop cluster onCassandra nodes, configuring a separate server for the Hadoop NameNode/JobTracker, and installinga Hadoop TaskTracker and Data Node on each Cassandra node. The nodes in the Cassandra datacenter can draw from data in the HDFS Data Node as well as from Cassandra. The Job Tracker/ResourceManager (JT/RM) receives MapReduce input from the client application. The JT/RM sends a MapReducejob request to the Task Trackers/Node Managers (TT/NM) and optional clients, MapReduce and Pig. Thedata is written to Cassandra and results sent back to the client.

The Apache docs also cover how to get configuration and integration support.

http://wiki.apache.org/cassandra/HadoopSupport

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Input and Output Formats

Hadoop jobs can receive data from CQL tables and indexes and you can load data into Cassandra from aHadoop job. Cassandra 2.1 supports the following formats for these tasks:

• CQL partition input format: ColumnFamilyInputFormat class.• BulkOutputFormat class introduced in Cassandra 1.1

Cassandra 2.1.1 and later supports the CqlOutputFormat, which is the CQL-compatible version of theBulkOutputFormat class. The CQLOutputFormat acts as a Hadoop-specific OutputFormat. Reduce taskscan store keys (and corresponding bound variable values) as CQL rows (and respective columns) in agiven CQL table.

Cassandra 2.1.1 supports using the CQLOutputFormat with Apache Pig.

Running the wordcount example

Wordcount example JARs are located in the examples directory of the Cassandra sourcecode installation. There are CQL and legacy examples in the hadoop_cql3_word_count andhadoop_word_count subdirectories, respectively. Follow instructions in the readme files.

Isolating Hadoop and Cassandra workloads

When you create a keyspace using CQL, Cassandra creates a virtual data center for a cluster, even a one-node cluster, automatically. You assign nodes that run the same type of workload to the same data center.The separate, virtual data centers for different types of nodes segregate workloads running Hadoop fromthose running Cassandra. Segregating workloads ensures that only one type of workload is active per datacenter. Separating nodes running a sequential data load, from nodes running any other type of workload,such as Cassandra real-time OLTP queries is a best practice.

http://www.datastax.com/docs/1.1/cluster_architecture/hadoop_integration

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Operations

Monitoring Cassandra

Monitoring a Cassandra cluster

Understanding the performance characteristics of your Cassandra cluster is critical to diagnosing issuesand planning capacity.

Cassandra exposes a number of statistics and management operations via Java Management Extensions(JMX). JMX is a Java technology that supplies tools for managing and monitoring Java applicationsand services. Any statistic or operation that a Java application has exposed as an MBean can then bemonitored or manipulated using JMX.

During normal operation, Cassandra outputs information and statistics that you can monitor using JMX-compliant tools, such as:

• The Cassandra nodetool utility• DataStax OpsCenter management console• JConsole

Using the same tools, you can perform certain administrative commands and operations such as flushingcaches or doing a node repair.

Monitoring using the nodetool utility

The nodetool utility is a command-line interface for monitoring Cassandra and performing routine databaseoperations. Included in the Cassandra distribution, nodetool and is typically run directly from an operationalCassandra node.

The nodetool utility supports the most important JMX metrics and operations, and includes other usefulcommands for Cassandra administration, such as the proxyhistogram command. This example shows theoutput from nodetool proxyhistograms after running 4,500 insert statements and 45,000 select statementson a three ccm node-cluster on a local computer.

$ nodetool proxyhistogramsproxy histogramsPercentile Read Latency Write Latency Range Latency (micros) (micros) (micros)50% 1502.50 375.00 446.0075% 1714.75 420.00 498.0095% 31210.25 507.00 800.2098% 36365.00 577.36 948.4099% 36365.00 740.60 1024.39Min 616.00 230.00 311.00Max 36365.00 55726.00 59247.00

For a summary of the ring and its current state of general health, use the status command. For example:

$ nodetool statusNote: Ownership information does not include topology; for complete information, specify a keyspaceDatacenter: datacenter1=======================Status=Up/Down|/ State=Normal/Leaving/Joining/Moving

http://www.datastax.com/products/opscenter

https://github.com/pcmanus/ccm

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-- Address Load Tokens Owns Host ID RackUN 127.0.0.1 47.66 KB 1 33.3% aaa1b7c1-6049-4a08-ad3e-3697a0e30e10 rack1UN 127.0.0.2 47.67 KB 1 33.3% 1848c369-4306-4874-afdf-5c1e95b8732e rack1UN 127.0.0.3 47.67 KB 1 33.3% 49578bf1-728f-438d-b1c1-d8dd644b6f7f rack1

The nodetool utility provides commands for viewing detailed metrics for tables, server metrics, andcompaction statistics:

• nodetool cfstats displays statistics for each table and keyspace.• nodetool cfhistograms provides statistics about a table, including read/write latency, row size,

column count, and number of SSTables.• nodetool netstats provides statistics about network operations and connections.• nodetool tpstats provides statistics about the number of active, pending, and completed tasks for

each stage of Cassandra operations by thread pool.

DataStax OpsCenter

DataStax OpsCenter is a graphical user interface for monitoring and administering all nodes in aCassandra cluster from one centralized console. DataStax OpsCenter is bundled with DataStax supportofferings. You can register for a free version for development or non-production use.

OpsCenter provides a graphical representation of performance trends in a summary view that is hardto obtain with other monitoring tools. The GUI provides views for different time periods as well asthe capability to drill down on single data points. Both real-time and historical performance data for aCassandra or DataStax Enterprise cluster are available in OpsCenter. OpsCenter metrics are captured andstored within Cassandra.

Within OpsCenter you can customize the performance metrics viewed to meet your monitoring needs.Administrators can also perform routine node administration tasks from OpsCenter. Metrics withinOpsCenter are divided into three general categories: table metrics, cluster metrics, and OS metrics. Formany of the available metrics, you can view aggregated cluster-wide information or view information on aper-node basis.


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Monitoring using JConsole

JConsole is a JMX-compliant tool for monitoring Java applications such as Cassandra. It is included withSun JDK 5.0 and higher. JConsole consumes the JMX metrics and operations exposed by Cassandra anddisplays them in a well-organized GUI. For each node monitored, JConsole provides these six separate tabviews:

• Overview

Displays overview information about the Java VM and monitored values.• Memory

Displays information about memory use.• Threads

Displays information about thread use.• Classes

Displays information about class loading.• VM Summary

Displays information about the Java Virtual Machine (VM).• Mbeans

Displays information about MBeans.

The Overview and Memory tabs contain information that is very useful for Cassandra developers.The Memory tab allows you to compare heap and non-heap memory usage, and provides a control toimmediately perform Java garbage collection.

For specific Cassandra metrics and operations, the most important area of JConsole is the MBeans tab.This tab lists the following Cassandra MBeans:

• org.apache.cassandra.db

Includes caching, table metrics, and compaction.• org.apache.cassandra.internal

Internal server operations such as gossip and hinted handoff.• org.apache.cassandra.net

Inter-node communication including FailureDetector, MessagingService and StreamingService.• org.apache.cassandra.request

Tasks related to read, write, and replication operations.

When you select an MBean in the tree, its MBeanInfo and MBean Descriptor are displayed on the right,and any attributes, operations or notifications appear in the tree below it. For example, selecting andexpanding the org.apache.cassandra.db MBean to view available actions for a table results in a display likethe following:

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If you choose to monitor Cassandra using JConsole, keep in mind that JConsole consumes a significantamount of system resources. For this reason, DataStax recommends running JConsole on a remotemachine rather than on the same host as a Cassandra node.

The JConsole CompactionManagerMBean exposes compaction metrics that can indicate when you needto add capacity to your cluster.

Compaction metrics

Monitoring compaction performance is an important aspect of knowing when to add capacity to yourcluster. The following attributes are exposed through CompactionManagerMBean:

Table 8: Compaction Metrics

Attribute Description

CompletedTasks Number of completed compactions since the laststart of this Cassandra instance

PendingTasks Number of estimated tasks remaining to perform

ColumnFamilyInProgress The table currently being compacted. This attributeis null if no compactions are in progress.

BytesTotalInProgress Total number of data bytes (index and filter are notincluded) being compacted. This attribute is null ifno compactions are in progress.

BytesCompacted The progress of the current compaction. Thisattribute is null if no compactions are in progress.

Thread pool and read/write latency statistics

Cassandra maintains distinct thread pools for different stages of execution. Each of the thread poolsprovide statistics on the number of tasks that are active, pending, and completed. Trends on these poolsfor increases in the pending tasks column indicate when to add additional capacity. After a baseline isestablished, configure alarms for any increases above normal in the pending tasks column. Use nodetooltpstats on the command line to view the thread pool details shown in the following table.


Thread Pool Description

AE_SERVICE_STAGE Shows anti-entropy tasks.

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Thread Pool Description

CONSISTENCY-MANAGER Handles the background consistency checks if theywere triggered from the client's consistency level.

FLUSH-SORTER-POOL Sorts flushes that have been submitted.

FLUSH-WRITER-POOL Writes the sorted flushes.

GOSSIP_STAGE Activity of the Gossip protocol on the ring.

LB-OPERATIONS The number of load balancing operations.

LB-TARGET Used by nodes leaving the ring.

MEMTABLE-POST-FLUSHER Memtable flushes that are waiting to be written tothe commit log.

MESSAGE-STREAMING-POOL Streaming operations. Usually triggered bybootstrapping or decommissioning nodes.

MIGRATION_STAGE Tasks resulting from the call of system_* methodsin the API that have modified the schema.

MISC_STAGE

MUTATION_STAGE API calls that are modifying data.

READ_STAGE API calls that have read data.

RESPONSE_STAGE Response tasks from other nodes to messagestreaming from this node.

STREAM_STAGE Stream tasks from this node.

Read/Write latency metrics

Cassandra tracks latency (averages and totals) of read, write, and slicing operations at the server levelthrough StorageProxyMBean.

Table statistics

For individual tables, ColumnFamilyStoreMBean provides the same general latency attributes asStorageProxyMBean. Unlike StorageProxyMBean, ColumnFamilyStoreMBean has a number of otherstatistics that are important to monitor for performance trends. The most important of these are:



MemtableDataSize The total size consumed by this table's data (notincluding metadata).

MemtableColumnsCount Returns the total number of columns present in thememtable (across all keys).

MemtableSwitchCount How many times the memtable has been flushedout.

RecentReadLatencyMicros The average read latency since the last call to thisbean.

RecentWriterLatencyMicros The average write latency since the last call to thisbean.

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LiveSSTableCount The number of live SSTables for this table.

The recent read latency and write latency counters are important in making sure operations are happeningin a consistent manner. If these counters start to increase after a period of staying flat, you probably needto add capacity to the cluster.

You can set a threshold and monitor LiveSSTableCount to ensure that the number of SSTables for a giventable does not become too great.

Tuning Bloom filtersCassandra uses Bloom filters to determine whether an SSTable has data for a particular row.

Bloom filters are unused for range scans, but are used for index scans. Bloom filters are probabilisticsets that allow you to trade memory for accuracy. This means that higher Bloom filter attributesettings bloom_filter_fp_chance use less memory, but will result in more disk I/O if the SSTablesare highly fragmented. Bloom filter settings range from 0 to 1.0 (disabled). The default value ofbloom_filter_fp_chance depends on the compaction strategy. The LeveledCompactionStrategy uses ahigher default value (0.1) than the SizeTieredCompactionStrategy or DateTieredCompactionStrategy,which have a default of 0.01. Memory savings are nonlinear; going from 0.01 to 0.1 saves about one thirdof the memory. SSTables using LCS contain a relatively smaller ranges of keys than those using STCS,which facilitates efficient exclusion of the SSTables even without a bloom filter; however, adding a smallbloom filter helps when there are many levels in LCS.

The settings you choose depend the type of workload. For example, to run an analytics application thatheavily scans a particular table, you would want to inhibit the Bloom filter on the table by setting it high.

To view the observed Bloom filters false positive rate and the number of SSTables consulted per read usecfstats in the nodetool utility.

Bloom filters are stored off-heap so you don't need include it when determining the -Xmx settings (themaximum memory size that the heap can reach for the JVM).

To change the bloom filter property on a table, use CQL. For example:

ALTER TABLE addamsFamily WITH bloom_filter_fp_chance = 0.1;

After updating the value of bloom_filter_fp_chance on a table, Bloom filters need to be regenerated in oneof these ways:

• Initiate compaction• Upgrade SSTables

You do not have to restart Cassandra after regenerating SSTables.

Data caching

Configuring data caches

Cassandra includes integrated caching and distributes cache data around the cluster. When a nodegoes down, the client can read from another cached replica of the data. The integrated architecture alsofacilitates troubleshooting because there is no separate caching tier, and cached data matches what’sin the database exactly. The integrated cache solves the cold start problem by saving the cache to diskperiodically. Cassandra reads contents back into the cache and distributes the data when it restarts. Thecluster does not start with a cold cache.

/documentation/cql/3.1/cql/cql_reference/tabProp.html?scroll=tabProp__moreBloomFilter


/documentation/cql/3.1/cql/cql_reference/tabProp.html?scroll=tabProp__moreBloomFilter

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In Cassandra 2.1, the saved key cache files include the ID of the table in the file name. A saved key cachefile name for the users table in the mykeyspace keyspace in a Cassandra 2.1 looks something like this:mykeyspace-users.users_name_idx-19bd7f80352c11e4aa6a57448213f97f-KeyCache-b.db2046071785672832311.tmp

You can configure partial or full caching of each partition by setting the rows_per_partition table option.Previously, the caching mechanism put the entire partition in memory. If the partition was larger than thecache size, Cassandra never read the data from the cache. Now, you can specify the number of rows tocache per partition to increase cache hits. You configure the cache using the CQL caching property.

About the partition key cache

The partition key cache is a cache of the partition index for a Cassandra table. Using the key cache insteadof relying on the OS page cache decreases seek times. However, enabling just the key cache results indisk (or OS page cache) activity to actually read the requested data rows.

About the row cache

You can configure the number of rows to cache in a partition. To cache rows, if the row key is not alreadyin the cache, Cassandra reads the first portion of the partition, and puts the data in the cache. If the newlycached data does not include all cells configured by user, Cassandra performs another read.

Typically, you enable either the partition key or row cache for a table, except archive tables, which areinfrequently read. Disable caching entirely for archive tables.

Enabling and configuring caching

About this task

Use CQL to enable or disable caching by configuring the caching table property. Set parameters in thecassandra.yaml file to configure global caching properties:

• Partition key cache size• Row cache size• How often Cassandra saves partition key caches to disk• How often Cassandra saves row caches to disk

Set the caching property using CREATE TABLE or ALTER TABLE. For example, configuring therow_cache_size_in_mb determines how much space in memory Cassandra allocates to store rows fromthe most frequently read partitions of the table.

Procedure

Set the table caching property that configures the partition key cache and the row cache.

CREATE TABLE users ( userid text PRIMARY KEY, first_name text, last_name text,)WITH caching = { 'keys' : 'NONE', 'rows_per_partition' : '120' };

How caching works

When both row cache and partition key cache are configured, the row cache returns results wheneverpossible. In the event of a row cache miss, the partition key cache might still provide a hit that makesthe disk seek much more efficient. This diagram depicts two read operations on a table with both cachesalready populated.

/documentation/cql/3.1/cql/cql_reference/tabProp.html?scroll=tabProp__moreCaching


/documentation/cql/3.1/cql/cql_reference/tabProp.html?scroll=tabProp__moreCaching

/documentation/cql/3.1/cql/cql_reference/refSetTabProp.html

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One read operation hits the row cache, returning the requested row without a disk seek. The other readoperation requests a row that is not present in the row cache but is present in the partition key cache. Afteraccessing the row in the SSTable, the system returns the data and populates the row cache with this readoperation.

Tips for efficient cache use

"Tuning the row cache in Cassandra 2.1" describes best practices of using the built-in cachingmechanisms and designing an effective data model. Some tips for efficient cache use are:

• Store lower-demand data or data with extremely long partitions in a table with minimal or no caching.• Deploy a large number of Cassandra nodes under a relatively light load per node.• Logically separate heavily-read data into discrete tables.

When you query a table, turn on tracing to check that the table actually gets data from the cache ratherthan from disk. The first time you read data from a partition, the trace shows this line below the querybecasue the cache has not been populated yet:

Row cache miss [ReadStage:41]

In subsequent queries for the same partition, look for a line in the trace that looks something like this:

Row cache hit [ReadStage:55]

This output means the data was found in the cache and no disk read occurred. Updates invalidate thecache. If you query rows in the cache plus uncached rows, request more rows than the global limit allows,or the query does not grab the beginning of the partition, the trace might include a line that looks somethinglike this:

Ignoring row cache as cached value could not satisfy query [ReadStage:89]

This output indicates that an insufficient cache caused a disk read. Requesting rows not at the beginningof the partition is a likely cause. Try removing constraints that might cause the query to skip the beginningof the partition, or place a limit on the query to prevent results from overflowing the cache. To ensure thatthe query hits the cache, try increasing the cache size limit, or restructure the table to position frequentlyaccessed rows at the head of the partition.

http://www.datastax.com/dev/blog/row-caching-in-cassandra-2-1

/documentation/cql/3.1/cql/cql_reference/tracing_r.html

/documentation/cql/3.1/cql/cql_reference/select_r.html?scroll=reference_ds_d35_v2q_xj__selAllFltr

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Monitoring and adjusting caching

Make changes to cache options in small, incremental adjustments, then monitor the effects of each changeusing DataStax Opscenter or the nodetool utility. The output of the nodetool info command shows thefollowing row cache and key cache metrics, which are configured in the cassandra.yaml file:

• Cache size in bytes• Capacity in bytes• Number of hits• Number of requests• Recent hit rate• Duration in seconds after which Cassandra saves the key cache.

For example, on start-up, the information from nodetool info might look something like this:

ID : 387d15ba-7103-491b-9327-1a691dbb504aGossip active : trueThrift active : trueNative Transport active: trueLoad : 65.87 KBGeneration No : 1400189757Uptime (seconds) : 148760Heap Memory (MB) : 392.82 / 1996.81Data Center : datacenter1Rack : rack1Exceptions : 0Key Cache : entries 10, size 728 (bytes), capacity 103809024 (bytes), 93 hits, 102 requests, 0.912 recent hit rate, 14400 save period in secondsRow Cache : entries 0, size 0 (bytes), capacity 0 (bytes), 0 hits, 0 requests, NaN recent hit rate, 0 save period in secondsCounter Cache : entries 0, size 0 (bytes), capacity 51380224 (bytes), 0 hits, 0 requests, NaN recent hit rate, 7200 save period in secondsToken : -9223372036854775808

In the event of high memory consumption, consider tuning data caches.

Configuring memtable throughputConfiguring memtable throughput can improve write performance. Cassandra flushes memtables to disk,creating SSTables when the commit log space threshold has been exceeded. Configure the commit logspace threshold per node in the cassandra.yaml. How you tune memtable thresholds depends on yourdata and write load. Increase memtable throughput under either of these conditions:

• The write load includes a high volume of updates on a smaller set of data.• A steady stream of continuous writes occurs. This action leads to more efficient compaction.

Allocating memory for memtables reduces the memory available for caching and other internal Cassandrastructures, so tune carefully and in small increments.

Configuring compaction

About this task

As discussed earlier, the compaction process merges keys, combines columns, evicts tombstones,consolidates SSTables, and creates a new index in the merged SSTable.

In the cassandra.yaml file, you configure these global compaction parameters:

• snapshot_before_compaction• in_memory_compaction_limit_in_mb


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• compaction_preheat_key_cache• concurrent_compactors• compaction_throughput_mb_per_sec

The compaction_throughput_mb_per_sec parameter is designed for use with large partitions becausecompaction is throttled to the specified total throughput across the entire system.

Cassandra provides a start-up option for testing compaction strategies without affecting the productionworkload.

Using CQL, you configure a compaction strategy:

• Size-tiered compaction• Date-tiered compaction• Leveled compaction

To configure the compaction strategy property and CQL compaction subproperties, such as the maximumnumber of SSTables to compact and minimum SSTable size, use CREATE TABLE or ALTER TABLE.

Procedure

1. Update a table to set the compaction strategy using the ALTER TABLE statement.

ALTER TABLE users WITH compaction = { 'class' : 'LeveledCompactionStrategy' }

2. Change the compaction strategy property to SizeTieredCompactionStrategy and specify the minimumnumber of SSTables to trigger a compaction using the CQL min_threshold attribute.

ALTER TABLE users WITH compaction = {'class' : 'SizeTieredCompactionStrategy', 'min_threshold' : 6 }

Results

You can monitor the results of your configuration using compaction metrics, see Compaction metrics.

CompressionCompression maximizes the storage capacity of Cassandra nodes by reducing the volume of data on diskand disk I/O, particularly for read-dominated workloads. Cassandra quickly finds the location of rows in theSSTable index and decompresses the relevant row chunks.

Write performance is not negatively impacted by compression in Cassandra as it is in traditionaldatabases. In traditional relational databases, writes require overwrites to existing data files on disk. Thedatabase has to locate the relevant pages on disk, decompress them, overwrite the relevant data, andfinally recompress. In a relational database, compression is an expensive operation in terms of CPU cyclesand disk I/O. Because Cassandra SSTable data files are immutable (they are not written to again afterthey have been flushed to disk), there is no recompression cycle necessary in order to process writes.SSTables are compressed only once when they are written to disk. Writes on compressed tables can showup to a 10 percent performance improvement.

When to compress data

Compression is best suited for tables that have many rows and each row has the same columns, or atleast as many columns, as other rows. For example, a table containing user data such as username, email,and state, is a good candidate for compression. The greater the similarity of the data across rows, thegreater the compression ratio and gain in read performance.

A table that has rows of different sets of columns is not well-suited for compression.




/documentation/cql/3.1/cql/cql_reference/create_table_r.html

/documentation/cql/3.1/cql/cql_reference/alter_table_r.html


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Don't confuse table compression with compact storage of columns, which is used for backwardcompatibility of old applications with CQL.

Depending on the data characteristics of the table, compressing its data can result in:

• 2x-4x reduction in data size• 25-35% performance improvement on reads• 5-10% performance improvement on writes

After configuring compression on an existing table, subsequently created SSTables are compressed.Existing SSTables on disk are not compressed immediately. Cassandra compresses existing SSTableswhen the normal Cassandra compaction process occurs. Force existing SSTables to be rewritten andcompressed by using nodetool upgradesstables (Cassandra 1.0.4 or later) or nodetool scrub.

Configuring compression

About this task

You configure a table property and subproperties to manage compression. The CQL table propertiesdocumentation describes the types of compression options that are available. Compression is enabled bydefault.

Procedure

1. Disable compression, using CQL to set the compression parameters to an empty string.

CREATE TABLE DogTypes ( block_id uuid, species text, alias text, population varint, PRIMARY KEY (block_id) ) WITH compression = { 'sstable_compression' : '' };

2. Enable compression on an existing table, using ALTER TABLE to set the compression algorithmsstable_compression to LZ4Compressor (Cassandra 1.2.2 and later), SnappyCompressor, orDeflateCompressor.

CREATE TABLE DogTypes ( block_id uuid, species text, alias text, population varint, PRIMARY KEY (block_id) ) WITH compression = { 'sstable_compression' : 'LZ4Compressor' };

3. Change compression on an existing table, using ALTER TABLE and setting the compression algorithmsstable_compression to DeflateCompressor.

ALTER TABLE CatTypes WITH compression = { 'sstable_compression' : 'DeflateCompressor', 'chunk_length_kb' : 64 }

You tune data compression on a per-table basis using CQL to alter a table.

/documentation/cql/3.1/cql/cql_reference/create_table_r.html

/documentation/cql/3.1/cql/cql_reference/tabProp.html?scroll=tabProp__moreCompression

/documentation/cql/3.1/cql/cql_reference/tabProp.html?scroll=tabProp__moreCompression

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Testing compaction and compression

About this task

Write survey mode is a Cassandra startup option for testing new compaction and compression strategies.In write survey mode, you can test out new compaction and compression strategies on that node andbenchmark the write performance differences, without affecting the production cluster.

Write survey mode adds a node to a database cluster. The node accepts all write traffic as if it were part ofthe normal Cassandra cluster, but the node does not officially join the ring.

Also use write survey mode to try out a new Cassandra version. The nodes you add in write survey modeto a cluster must be of the same major release version as other nodes in the cluster. The write surveymode relies on the streaming subsystem that transfers data between nodes in bulk and differs from onemajor release to another.

If you want to see how read performance is affected by modifications, stop the node, bring it up as astandalone machine, and then benchmark read operations on the node.

Procedure

Enable write survey mode by starting a Cassandra node using the write_survey option.

bin/cassandra – Dcassandra.write_survey=true

This example shows how to start a tarball installation of Cassandra.

Tuning Java resourcesConsider tuning Java resources in the event of a performance degradation or high memory consumption.

There are two files that control environment settings for Cassandra:

• conf/cassandra-env.sh

Java Virtual Machine (JVM) configuration settings• bin/cassandra-in.sh

Sets up Cassandra environment variables such as CLASSPATH and JAVA_HOME.

Heap sizing options

If you decide to change the Java heap sizing, both MAX_HEAP_SIZE and HEAP_NEWSIZE should shouldbe set together in conf/cassandra-env.sh.

• MAX_HEAP_SIZE

Sets the maximum heap size for the JVM. The same value is also used for the minimum heap size. Thisallows the heap to be locked in memory at process start to keep it from being swapped out by the OS.

• HEAP_NEWSIZE

The size of the young generation. The larger this is, the longer GC pause times will be. The shorter it is,the more expensive GC will be (usually). A good guideline is 100 MB per CPU core.

Tuning the Java heap

Because Cassandra is a database, it spends significant time interacting with the operating system'sI/O infrastructure through the JVM, so a well-tuned Java heap size is important. Cassandra's defaultconfiguration opens the JVM with a heap size that is based on the total amount of system memory:

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System Memory Heap Size

Less than 2GB 1/2 of system memory

2GB to 4GB 1GB

Greater than 4GB 1/4 system memory, but not more than 8GB

Many users new to Cassandra are tempted to turn up Java heap size too high, which consumes themajority of the underlying system's RAM. In most cases, increasing the Java heap size is actuallydetrimental for these reasons:

• In most cases, the capability of Java to gracefully handle garbage collection above 8GB quicklydiminishes.

• Modern operating systems maintain the OS page cache for frequently accessed data and are very goodat keeping this data in memory, but can be prevented from doing its job by an elevated Java heap size.

If you have more than 2GB of system memory, which is typical, keep the size of the Java heap relativelysmall to allow more memory for the page cache.

Some Solr users have reported that increasing the stack size improves performance under Tomcat. Toincrease the stack size, uncomment and modify the default setting in the cassandra-env.sh file. Also,decreasing the memtable space to make room for Solr caches might improve performance. Modify thememtable space using the memtable_total_space_in_mb property in the cassandra.yaml file.

Because MapReduce runs outside the JVM, changes to the JVM do not affect Analytics/Hadoopoperations directly.

How Cassandra uses memory

Using a java-based system like Cassandra, you can typically allocate about 8GB of memory on the heapbefore garbage collection pause time starts to become a problem. Modern machines have much morememory than that and Cassandra can make use of additional memory as page cache when files on diskare accessed. Allocating more than 8GB of memory on the heap poses a problem due to the amount ofCassandra metadata about data on disk. The Cassandra metadata resides in memory and is proportionalto total data. Some of the components grow proportionally to the size of total memory.

In Cassandra 1.2 and later, the Bloom filter and compression offset map that store this metadata reside off-heap, greatly increasing the capacity per node of data that Cassandra can handle efficiently. The partitionsummary also resides off-heap.

About the off-heap row cache

Cassandra can store cached rows in native memory, outside the Java heap. This results in both a smallerper-row memory footprint and reduced JVM heap requirements, which helps keep the heap size in thesweet spot for JVM garbage collection performance.

Tuning Java garbage collection

Cassandra's GCInspector class logs information about garbage collection whenever a garbage collectiontakes longer than 200ms. Garbage collections that occur frequently and take a moderate length of timeto complete (such as ConcurrentMarkSweep taking a few seconds), indicate that there is a lot of garbagecollection pressure on the JVM. Remedies include adding nodes, lowering cache sizes, or adjusting theJVM options regarding garbage collection.

JMX options

Cassandra exposes a number of statistics and management operations via Java Management Extensions(JMX). Java Management Extensions (JMX) is a Java technology that supplies tools for managing andmonitoring Java applications and services. Any statistic or operation that a Java application has exposed

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as an MBean can then be monitored or manipulated using JMX. JConsole, the nodetool utility, andDataStax OpsCenter are examples of JMX-compliant management tools.

By default, you can modify the following properties in the conf/cassandra-env.sh file to configure JMX tolisten on port 7199 without authentication.

• com.sun.management.jmxremote.port

The port on which Cassandra listens from JMX connections.• com.sun.management.jmxremote.ssl

Enable/disable SSL for JMX.• com.sun.management.jmxremote.authenticate

Enable/disable remote authentication for JMX.• -Djava.rmi.server.hostname

Sets the interface hostname or IP that JMX should use to connect. Uncomment and set if you arehaving trouble connecting.

Purging gossip state on a node

About this task

Gossip information is persisted locally by each node to use immediately on node restart without having towait for gossip communications.

Procedure

In the unlikely event you need to correct a problem in the gossip state:

1. Using MX4J or JConsole, connect to the node's JMX port and then use the JMX methodGossiper.unsafeAssassinateEndpoints(ip_address) to assassinate the problem node.

This takes a few seconds to complete so wait for confirmation that the node is deleted.

2. If the JMX method above doesn't solve the problem, stop your client application from sending writes tothe cluster.

3. Take the entire cluster offline:

a) Drain each node.

$ nodetool options drainb) Stop each node:

• Package installations:

$ sudo service cassandra stop• Tarball installations:

$ sudo service cassandra stop

4. Clear the data from the peers directory:

$ sudo rm -r /var/lib/cassandra/data/system/peers/*

5. Clear the gossip state when the node starts:

• For tarball installations, you can use a command line option or edit the cassandra-env.sh. To usethe command line:

$ install_location/bin/cassandra -Dcassandra.load_ring_state=false

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• For package installations or if you are not using the command line option above, add the followingline to the cassandra-env.sh file:

JVM_OPTS="$JVM_OPTS -Dcassandra.load_ring_state=false"

• Package installations: /usr/share/cassandra/cassandra-env.sh• Tarball installations: install_location/conf/cassandra-env.sh

6. Bring the cluster online one node at a time, starting with the seed nodes.


$ sudo service cassandra start• Tarball installations:


What to do nextRemove the line you added in the cassandra-env.sh file.

Repairing nodes

Node repair makes data on a replica consistent with data on other nodes. Anti-entropy node repairs areimportant for every Cassandra cluster. Frequent data deletions and a node going down are commoncauses of inconsistency. You use the nodetool repair command to repair a node. There are several typesof node repair, for example:

• Incremental• Partitioner range• Endpoint range

By default repairs are sequential, one node is repaired after another, and done in full, all SSTables arerepaired. You can combine repair options, such as parallel and incremental repair. This combination doesan incremental repair to all nodes at the same time. You can restrict repairs to local or other data centersor to nodes between a certain token range. You can specify which nodes have the good data to use toreplace the outdated data.

Incremental repair

The repair process involves computing a Merkle tree for each range of data on that node. The Merkle treeis a binary tree of hashes used by Cassandra for calculating the differences in datasets between nodes ina cluster. Each node involved in the repair has to construct its Merkle tree from all the SSTables it stores,making the calculation very expensive.

To reduce the expense of constructing trees, Cassandra 2.1 introduces a new type of repair, theincremental repair. An incremental repair makes already repaired data persistent, and only calculates aMerkle tree for unrepaired SSTables.

http://en.wikipedia.org/wiki/Merkle_tree

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Reducing the size of the Merkle tree improves the performance of the incremental repair process,assuming repairs are run frequently.

Incremental repairs begin with the repair leader sending out a prepare message to its peers. Each nodebuilds a Merkle tree from the unrepaired SStables. After the leader receives a Merkle tree from each node,the leader compares the trees and issues streaming requests. Finally, the leader issues an anticompactioncommand.

For more information about incremental repairs, see the "More efficient repairs" article.

Anticompaction

Anticompaction in Cassandra 2.1 is the process of segregating repaired and unrepaired ranges intoseparate SSTables unless the SSTable fits entirely within the repaired range. If the SSTable fits within therepaired range, Cassandra just updates the SSTable metadata.

Anticompaction occurs after an incremental repair. Cassandra performs anticompaction only on theSSTables that have a range of unrepaired data. If all node ranges are repaired, anticompaction does notneed to rewrite any data. During anticompaction, size/date-tiered compaction and leveled compactionhandle the segregation of the data differently.

• Size-tiered and date-tiered compaction splits repaired and unrepaired into separate pools for separatecompactions. A major compaction generates two SSTables, one containing repaired data and onecontaining unrepaired data.

• Leveled compaction performs size-tiered compaction on unrepaired data. After repair completes,Cassandra moves data from the set of unrepaired SSTables to L0.

Sequential versus parallel repair

By default, Cassandra 2.1 does a sequential repair of all SSTables, constructing the Merkle trees forone node after the other. Cassandra takes a snapshot of each replica immediately and then sequentially

http://www.datastax.com/dev/blog/more-efficient-repairs

http://planetcassandra.org/blog/post/anticompaction-in-cassandra-2-1/

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repairs each replica from the snapshots. For example, if you have RF=3 and A, B and C represents threereplicas, this command takes a snapshot of each replica immediately and then sequentially repairs eachreplica from the snapshots (A<->B, A<->C, B<->C).

A parallel repair does the repair of nodes A, B, and C all at once. During this type of repair, the dynamicsnitch maintains performance for your application using a replica in the snapshot that is not undergoingrepair.

Snapshots are hardlinks to existing SSTables. Snapshots are immutable and require almost no disk space.Repair requires intensive disk I/O because validation compaction occurs during Merkle tree construction.For any given replica set, only one replica at a time performs the validation compaction.

Partitioner range repair

Using the nodetool repair -pr (–partitioner-range) option repairs only the first range returned by thepartitioner for a node. Other replicas for that range still have to perform the Merkle tree calculation, causinga validation compaction. Because all the replicas are compacting at the same time, all the nodes may beslow to respond for that portion of the data. This type of repair operates on each node in the cluster insuccession without duplicating work.

Merkle trees do not have infinite resolution and Cassandra makes a tradeoff between the size and space.Currently, Cassandra uses a fixed depth of 15 for the tree (32K leaf nodes). For a node containing a millionpartitions with one damaged partition, about 30 partitions are streamed, which is the number that fall intoeach of the leaves of the tree. The problem gets worse when more partitions exist per node, and resultsin significant disk space usage and needless compaction. Generally, partitioner range repairs are notrecommended.

Repairing a subrange

To mitigate overstreaming, you can use subrange repair, but generally subrange repairs are notrecommended. A subrange repair does a portion of the data belonging to the node. Because the Merkletree precision is fixed, this effectively increases the overall precision.

To use subrange repair:

1. Use the Java describe_splits call to ask for a split containing 32K partitions.2. Iterate throughout the entire range incrementally or in parallel. This completely eliminates the

overstreaming behavior and wasted disk usage overhead.3. Pass the tokens you received for the split to the nodetool repair -st (–start-token) and -et (–end-

token) options.4. Pass the -local (–in-local-dc) option to nodetool to repair only within the local data center. This reduces

the cross data-center transfer load.

Repair guidelines

Run repair in these situations:

• Daily if you run incremental repairs, weekly if you run full repairs.

Note: Even if deletions never occur, schedule regular repairs. Setting a column to null is adelete.

• During node recovery. For example, when bringing a node back into the cluster after a failure.• On nodes containing data that is not read frequently.• To update data on a node that has been down.• To recover missing data or corrupted SSTables. A non-incremental is required.

Guidelines for running routine node repair include:

• A full repair is recommended to eliminate the need for anticompaction.• Migrating to incremental repairs is recommended if you use leveled compaction.



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• The hard requirement for routine repair frequency is the value of gc_grace_seconds. Run a repairoperation at least once on each node within this time period. Following this important guideline ensuresthat deletes are properly handled in the cluster.

• Use caution when running routine node repair on more than one node at a time and schedule regularrepair operations for low-usage hours.

• In systems that seldom delete or overwrite data, you can raise the value of gc_grace_seconds withminimal impact to disk space. A higher value schedules wider intervals between repair operations.

• To mitigate heavy disk usage, configure nodetool compaction throttling options(setcompactionthroughput and setcompactionthreshold) before running a repair.

Migrating to incremental repairs

Migrating to incremental repairs by using the sstablerepaired set utility is recommended only under thefollowing conditions:

• You are doing an incremental repair for the first time.• You are using the leveled compaction strategy.

Full, sequential repairs are the default because until the first incremental repair, Cassandra does notknow the repaired state of SSTables. After an incremental repair, anticompaction marks SSTables asrepaired or not. If you use the leveled compaction strategy and perform an incremental repair for the firsttime, Cassandra performs size-tiering on all SSTables because the repair/unrepaired status is unknown.This operation can take a long time. To save time, migrate to incremental repair one node at a time. Themigration procedure, covered in the next section, uses utilities in the tools/bin directory of installationsother than RHEL and Debian:

• sstablemetadata for checking the repaired or unrepaired status of an SSTable• sstablerepairedset for manually marking an SSTable as repaired

The syntax of these commands is:

sstablemetadata <sstable filenames>

sstablerepairedset [--is-repaired | --is-unrepaired] [-f <sstable-list> | <sstables>]

In Cassandra 2.1.1, sstablerepairedset can take as arguments a list of SSTables on the commandline or a file SSTables with a "-f" flag.

Note: In RHEL and Debian installations, you must install the tools packages.

This example shows how to use sstablerepairedset to clear the repaired state of an SSTable, rendering theSSTable unrepaired.

1. Stop the node.2. Run this command:

sstablerepairedset --is-unrepaired -f list_of_sstable_names.txt3. Restart the node.

All data is changed to an unrepaired state.

Procedure for migrating to incremental repairs

To migrate to incremental repair, one node at a time:

1. Disable compaction on the node using nodetool disableautocompaction.2. Run the default full, sequential repair.3. Stop the node.4. Use the tool sstablerepairedset to mark all the SSTables that were created before you disabled

compaction.5. Restart cassandra


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SSTables remain in a repaired state after running a full, but not a partition range, repair if you make nochanges to the SSTables.

Adding or removing nodes, data centers, or clusters

Adding nodes to an existing clusterSteps to add nodes when using virtual nodes.

About this task

Virtual nodes (vnodes) greatly simplify adding nodes to an existing cluster:

• Calculating tokens and assigning them to each node is no longer required.• Rebalancing a cluster is no longer necessary because a node joining the cluster assumes responsibility

for an even portion of the data.

For a detailed explanation about how vnodes work, see Virtual nodes.

If you are using racks, you can safely bootstrap two nodes at a time when both nodes are on the samerack.

Note: If you do not use vnodes, use OpsCenter to add capacity. You can also use the instructionsin the Cassandra 1.1 topic Adding Capacity to an Existing Cluster.

Procedure

1. Install Cassandra on the new nodes, but do not start Cassandra.

If you used the Debian install, Cassandra starts automatically and you must stop the node and clear thedata.

2. Set the following properties in the cassandra.yaml and, depending on the snitch, the cassandra-topology.properties or cassandra-rackdc.properties configuration files:

• auto_bootstrap - If this option has been set to false, you must set it to true. This option is not listed inthe default cassandra.yaml configuration file and defaults to true.

• cluster_name - The name of the cluster the new node is joining.• listen_address/broadcast_address - Can usually be left blank. Otherwise, use IP address or host

name that other Cassandra nodes use to connect to the new node.• endpoint_snitch - The snitch Cassandra uses for locating nodes and routing requests.• num_tokens - The number of vnodes to assign to the node. If the hardware capabilities vary among

the nodes in your cluster, you can assign a proportional number of vnodes to the larger machines.• seed_provider - The -seeds list in this setting determines which nodes the new node should contact

to learn about the cluster and establish the gossip process.

Note: Seed nodes cannot bootstrap. Make sure the new node is not listed in the -seeds list.Do not make all nodes seed nodes. Please read Internode communications (gossip).

• Change any other non-default settings you have made to your existing cluster in thecassandra.yaml file and cassandra-topology.properties or cassandra-rackdc.properties files. Use the diff command to find and merge (by head) any differencesbetween existing and new nodes.

3. Use nodetool status to verify that the node is fully bootstrapped and all other nodes are up (UN) and notin any other state.

4. After all new nodes are running, run nodetool cleanup on each of the previously existing nodes toremove the keys that no longer belong to those nodes. Wait for cleanup to complete on one nodebefore running nodetool cleanup on the next node.

Cleanup can be safely postponed for low-usage hours.

/documentation/latest-opsc/

http://www.datastax.com/docs/1.1/cluster_management#adding-capacity-to-an-existing-cluster

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Note: Consistency issues might result when more than one node is added at a time. To assessthe risks to your environment, see JIRA issues CASSANDRA-2434 and CASSANDRA-7069.Although adding multiple nodes at the same time is not a best practice, you can reduce dataconsistency risks by following these steps:

1. Before you add the nodes, turn off consistent range movements with the -Dconsistent.rangemovement=false property.

Package installations

Add the following option to the /usr/share/cassandra/cassandra-env.sh file:

JVM_OPTS="$JVM_OPTS -Dconsistent.rangemovement=false

Tarball installations

Start Cassandra with this option:

$ bin/cassandra -Dconsistent.rangemovement=false

2. Allow two minutes between node initializations.3. After the nodes are added, turn consistent range movement back on.

Adding a data center to a clusterSteps to add a data center to an existing cluster.

Procedure

1. Ensure that you are using NetworkTopologyStrategy for all of your keyspaces.

2. For each node, set the following properties in the cassandra.yaml file:

a) Add (or edit) auto_bootstrap: false.

By default, this setting is true and not listed in the cassandra.yaml file. Setting this parameter tofalse prevents the new nodes from attempting to get all the data from the other nodes in the datacenter. When you run nodetool rebuild in the last step, each node is properly mapped.

b) Set other properties, such as -seeds and endpoint_snitch, to match the cluster settings.

For more guidance, see Initializing a multiple node cluster (multiple data centers).

Note: Do not make all nodes seeds, see Internode communications (gossip).

c) If you want to enable vnodes, set num_tokens.

The recommended value is 256. Do not set the initial_token parameter.

3. Update the relevant property file for snitch used on all servers to include the new nodes. You do notneed to restart.

• GossipingPropertyFileSnitch: cassandra-rackdc.properties• PropertyFileSnitch: cassandra-topology.properties

4. Ensure that your clients are configured correctly for the new cluster:

• If your client uses the DataStax Java, C#, or Python driver, set the load-balancing policy toDCAwareRoundRobinPolicy (Java, C#, Python).

• If you are using another client such as Hector, make sure it does not auto-detect the new nodes sothat they aren't contacted by the client until explicitly directed. For example if you are using Hector,use sethostConfig.setAutoDiscoverHosts(false);. If you are using Astyanax, useConnectionPoolConfigurationImpl.setLocalDatacenter("<data center name">) toensure you are connecting to the specified data center.

• If you are using Astyanax 2.x, with integration with the DataStax Java Driver 2.0,you can set the load-balancing policy to DCAwareRoundRobinPolicy by callingJavaDriverConfigBuilder.withLoadBalancingPolicy().

AstyanaxContext<Keyspace> context = new AstyanaxContext.Builder()



http://www.datastax.com/drivers/java/2.0/com/datastax/driver/core/policies/DCAwareRoundRobinPolicy.html

http://www.datastax.com/drivers/csharp/apidocs/html/74972c38-2e00-0ecd-e8c1-7247e6e6f820.htm

http://datastax.github.io/python-driver/api/cassandra/policies.html#cassandra.policies.DCAwareRoundRobinPolicy

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... .withConnectionPoolConfiguration(new JavaDriverConfigBuilder() .withLoadBalancingPolicy(new TokenAwarePolicy(new DCAwareRoundRobinPolicy())) .build()) ...

5. If using a QUORUM consistency level for reads or writes, check the LOCAL_QUORUM orEACH_QUORUM consistency level to see if the level meets your requirements for multiple datacenters.

6. Start Cassandra on the new nodes.

7. After all nodes are running in the cluster:

a) Change the keyspace properties to specify the desired replication factor for the new data center.

For example, set strategy options to DC1:2, DC2:2.

For more information, see ALTER KEYSPACE.b) Run nodetool rebuild specifying the existing data center on all nodes in the new data center:

nodetool rebuild -- name_of_existing_data_center

Otherwise, requests to the new data center with LOCAL_ONE or ONE consistency levels may fail ifthe existing data centers are not completely in-sync.

You can run rebuild on one or more nodes at the same time. The choices depends on whether yourcluster can handle the extra IO and network pressure of running on multiple nodes. Running on onenode at a time has the least impact on the existing cluster.

Attention: If you don't specify the existing data center in the command line, the new nodeswill appear to rebuild successfully, but will not contain any data.

8. Change to true or remove auto_bootstrap: false in the cassandra.yaml file.

Returns this parameter to its normal setting so the nodes can get all the data from the other nodes inthe data center if restarted.

Replacing a dead node or dead seed nodeSteps to replace a node that has died for some reason, such as hardware failure.

Replacing a dead seed node

1. Promote an existing node to a seed node by adding its IP address to -seeds list and remove (demote)the IP address of the dead seed node from the cassandra.yaml file for each node in the cluster.

2. Replace the dead node, as described in the next section.

Replacing a dead node

You must prepare and start the replacement node, integrate it into the cluster, and then remove the deadnode.

Procedure

1. Confirm that the node is dead using nodetool status:

The nodetool command shows a down status for the dead node (DN):

2. Note the Address of the dead node; it is used in step 5.


/documentation/cql/3.1/cql/cql_reference/alter_keyspace_r.html

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3. Install Cassandra on the new node, but do not start Cassandra.

If you used the Debian/Ubuntu install, Cassandra starts automatically and you must and stop the nodeand clear the data.

4. Set the following properties in the cassandra.yaml and, depending on the snitch, the cassandra-topology.properties or cassandra-rackdc.properties configuration files:

• auto_bootstrap - If this option has been set to false, you must set it to true. This option is not listed inthe default cassandra.yaml configuration file and defaults to true.

• cluster_name - The name of the cluster the new node is joining.• listen_address/broadcast_address - Can usually be left blank. Otherwise, use IP address or host

name that other Cassandra nodes use to connect to the new node.• endpoint_snitch - The snitch Cassandra uses for locating nodes and routing requests.• num_tokens - The number of vnodes to assign to the node. If the hardware capabilities vary among

the nodes in your cluster, you can assign a proportional number of vnodes to the larger machines.• seed_provider - The -seeds list in this setting determines which nodes the new node should contact

to learn about the cluster and establish the gossip process.

Note: Seed nodes cannot bootstrap. Make sure the new node is not listed in the -seeds list.Do not make all nodes seed nodes. Please read Internode communications (gossip).

• Change any other non-default settings you have made to your existing cluster in thecassandra.yaml file and cassandra-topology.properties or cassandra-rackdc.properties files. Use the diff command to find and merge (by head) any differencesbetween existing and new nodes.

5. Start the replacement node with the replace_address option:

• Package installations: Add the following option to /usr/share/cassandra/cassandra-env.shfile:

JVM_OPTS="$JVM_OPTS -Dcassandra.replace_address=address_of_dead_node• Tarball installations: Start Cassandra with this option:

$ sudo bin/cassandra -Dcassandra.replace_address=address_of_dead_node

6. If using a packaged install, after the new node finishes bootstrapping, remove the option you added instep 5.

What to do next

Remove the old node's IP address from the cassandra-topology.properties or cassandra-rackdc.properties file

Caution: Wait at least 72 hours to ensure that old node information is removed from gossip. Ifremoved from the property file too soon, problems may result.

Replacing a running nodeSteps to replace a node with a new node, such as when updating to newer hardware or performingproactive maintenance.

About this task

You must prepare and start the replacement node, integrate it into the cluster, and then decommision theold node.

Note: To change the IP address of a node, simply change the IP of node and then restartCassandra. If you change the IP address of a seed node, you must update the -seeds parameter inthe seed_provider for each node in the cassandra.yaml file.

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Procedure

1. Prepare and start the replacement node, as described in Adding nodes to an existing cluster.

Note: If not using vnodes, see Adding Capacity to an Existing Cluster in the Cassandra 1.1documentation.

2. Confirm that the replacement node is alive:

• Run nodetool ring if not using vnodes.• Run nodetool status if using vnodes.

The status should show:

• nodetool ring: Up• nodetool status: UN

3. Note the Host ID of the node; it is used in the next step.

4. Using the Host ID of the original node, decommission the original node from the cluster using thenodetool decommission command.

Decommissioning a data centerSteps to properly remove a data center so no information is lost.

About this task

Procedure

1. Make sure no clients are still writing to any nodes in the data center.

2. Run a full repair with nodetool repair.

This ensures that all data is propagated from the data center being decommissioned.

3. Change all keyspaces so they no longer reference the data center being removed.

4. Run nodetool decommission on every node in the data center being removed.

Removing a nodeReduce the size of a data center.

About this taskUse these instructions when you want to remove nodes to reduce the size of your cluster, not for replacinga dead node.

Attention: If you are not using virtual nodes (vnodes), you must rebalance the cluster.

Procedure

1. Check whether the node is up or down using nodetool status:

The nodetool command shows the status of the node (UN=up, DN=down):

2. If the node is up, run nodetool decommission.

This assigns the ranges that the node was responsible for to other nodes and replicates the dataappropriately.

Use nodetool netstats to monitor the progress.

http://www.datastax.com/docs/1.1/cluster_management#adding-capacity-to-an-existing-cluster

/documentation/cql/3.1/cql/cql_reference/alter_keyspace_r.html

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3. If the node is down:

• If the cluster uses vnodes, remove the node using the nodetool removenode command.• If the cluster does not use vnodes, before running the nodetool removenode command, adjust your

tokens to evenly distribute the data across the remaining nodes to avoid creating a hot spot. See thefollowing in the Cassandra 1.1 documentation:

• About Data Partitioning in Cassandra• Generating Tokens

Switching snitches

About this task

Because snitches determine how Cassandra distributes replicas, the procedure to switch snitches dependson whether or not the topology of the cluster will change:

• If data has not been inserted into the cluster, there is no change in the network topology. This meansthat you only need to set the snitch; no other steps are necessary.

• If data has been inserted into the cluster, it's possible that the topology has changed and you will needto perform additional steps.

A change in topology means that there is a change in the data centers and/or racks where the nodes areplaced. Topology changes may occur when the replicas are placed in different places by the new snitch.Specifically, the replication strategy places the replicas based on the information provided by the newsnitch. The following examples demonstrate the differences:

• No topology change

Suppose you have 5 nodes using the SimpleSnitch in a single data center and you change to 5 nodesin 1 data center and 1 rack using a network snitch such as the GossipingPropertyFileSnitch.

• Topology change

Suppose you have 5 nodes using the SimpleSnitch in a single data center and you change to 5 nodesin 2 data centers using the PropertyFileSnitch.

Note: If splitting from one data center to two, you need to change the schema for the keyspacethat are splitting. Additionally, the data center names must change accordingly.

• Topology change

Suppose you have 5 nodes using the SimpleSnitch in a single data center and you change to 5 nodesin 1 data center and 2 racks using the RackInferringSnitch.

The configuration files for snitches are located in:

• Tarball installations: install_location/conf• Package installations: /etc/cassandra

Procedure

1. Create a properties file with data center and rack information.

• cassandra-rackdc.properties - GossipingPropertyFileSnitch, EC2Snitch, andEC2MultiRegionSnitch only

• cassandra-topology.properties - all other network snitches

2. Copy the cassandra-topology.properties or cassandra-rackdc.properties file to theCassandra configuration directory on all the cluster's nodes. They won't be used until the new snitch isenabled.

3. Change the snitch for each node in the cluster in the node's cassandra.yaml file. For example:

endpoint_snitch: GossipingPropertyFileSnitch

http://www.datastax.com/docs/1.1/cluster_architecture/partitioning#about-data-partitioning-in-cassandra

http://www.datastax.com/docs/1.1/initialize/token_generation#generating-tokens


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4. If the topology has not changed, you can restart each node one at a time.

Any change in the cassandra.yaml file requires a node restart.

5. If the topology of the network has changed:

a) Shut down all the nodes, then restart them.b) Run a sequential repair and nodetool cleanup on each node.

Edge cases for transitioning or migrating a clusterUnusual migration scenarios without interruption of service.

About this task

The information in this topic is intended for the following types of scenarios (without any interruption ofservice):

• Transition a cluster on EC2 to a cluster on Amazon virtual private cloud (VPC).• Migrate from a cluster when the network separates the current cluster from the future location.• Migrate from an early Cassandra cluster to a recent major version.

Procedure

The following method ensures that if something goes wrong with the new cluster, you still have the existingcluster until you no longer need it.

1. Set up and configure the new cluster as described in Provisioning a new cluster.

Note: If you're not using vnodes, be sure to configure the token ranges in the new nodes tomatch the ranges in the old cluster.

2. Set up the schema for the new cluster using CQL.

3. Configure your client to write to both clusters.

Depending on how the writes are done, code changes may be needed. Be sure to use identicalconsistency levels.

4. Ensure that the data is flowing to the new nodes so you won't have any gaps when you copy thesnapshots to the new cluster in step 6.

5. Snapshot the old EC2 cluster.

6. Copy the data files from your keyspaces to the nodes.

• If not using vnodes and the if the node ratio is 1:1, it's simpler and more efficient to simply copy thedata files to their matching nodes.

• If the clusters are different sizes or if you are using vnodes, use the Cassandra bulk loader(sstableloader) (sstableloader).

7. You can either switch to the new cluster all at once or perform an incremental migration.

For example, to perform an incremental migration, you can set your client to designate a percentage ofthe reads that go to the new cluster. This allows you to test the new cluster before decommissioning theold cluster.

8. Decommission the old cluster:

a) Remove the cluster from the OpsCenter.b) Remove the nodes.


/documentation/cql/3.1/cql/cql_using/about_cql_c.html

/documentation/opscenter/5.0/opsc/online_help/opscRemovingCluster_t.html

Backing up and restoring data

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Cassandra backs up data by taking a snapshot of all on-disk data files (SSTable files) stored in the datadirectory.

You can take a snapshot of all keyspaces, a single keyspace, or a single table while the system is online.

Using a parallel ssh tool (such as pssh), you can snapshot an entire cluster. This provides an eventuallyconsistent backup. Although no one node is guaranteed to be consistent with its replica nodes at the timea snapshot is taken, a restored snapshot resumes consistency using Cassandra's built-in consistencymechanisms.

After a system-wide snapshot is performed, you can enable incremental backups on each node to backupdata that has changed since the last snapshot: each time an SSTable is flushed, a hard link is copied into a/backups subdirectory of the data directory (provided JNA is enabled).

Note: If JNA is enabled, snapshots are performed by hard links. If not enabled, I/O activityincreases as the files are copied from one location to another, which significantly reduces efficiency.

Taking a snapshot

About this task

Snapshots are taken per node using the nodetool snapshot command. To take a global snapshot, run thenodetool snapshot command using a parallel ssh utility, such as pssh.

A snapshot first flushes all in-memory writes to disk, then makes a hard link of the SSTable files for eachkeyspace. You must have enough free disk space on the node to accommodate making snapshots of yourdata files. A single snapshot requires little disk space. However, snapshots can cause your disk usage togrow more quickly over time because a snapshot prevents old obsolete data files from being deleted. Afterthe snapshot is complete, you can move the backup files to another location if needed, or you can leavethem in place.

Note: Cassandra can only restore data from a snapshot when the table schema exists. It isrecommended that you also backup the schema.

Procedure

Run the nodetool snapshot command, specifying the hostname, JMX port, and keyspace. For example:

$ nodetool -h localhost -p 7199 snapshot mykeyspace

Results

The snapshot is created in data_directory_location/keyspace_name/table_name-UUID/snapshots/snapshot_name directory. Each snapshot directory contains numerous .db files thatcontain the data at the time of the snapshot.

For example:


/var/lib/cassandra/data/mykeyspace/users-081a1500136111e482d09318a3b15cc2/snapshots/1406227071618/mykeyspace-users-ka-1-Data.db


install_location/data/data/mykeyspace/users-081a1500136111e482d09318a3b15cc2/snapshots/1406227071618/mykeyspace-users-ka-1-Data.db


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Deleting snapshot files

About this task

When taking a snapshot, previous snapshot files are not automatically deleted. You should remove oldsnapshots that are no longer needed.

The nodetool clearsnapshot command removes all existing snapshot files from the snapshot directory ofeach keyspace. You should make it part of your back-up process to clear old snapshots before taking anew one.

Procedure

To delete all snapshots for a node, run the nodetool clearsnapshot command. For example:

$ nodetool -h localhost -p 7199 clearsnapshot

To delete snapshots on all nodes at once, run the nodetool clearsnapshot command using a parallelssh utility.

Enabling incremental backups

About this task

When incremental backups are enabled (disabled by default), Cassandra hard-links each flushed SSTableto a backups directory under the keyspace data directory. This allows storing backups offsite withouttransferring entire snapshots. Also, incremental backups combine with snapshots to provide a dependable,up-to-date backup mechanism.

As with snapshots, Cassandra does not automatically clear incremental backup files. DataStaxrecommends setting up a process to clear incremental backup hard-links each time a new snapshot iscreated.

Procedure

Edit the cassandra.yaml configuration file on each node in the cluster and change the value ofincremental_backups to true.

Restoring from a Snapshot

About this task

Restoring a keyspace from a snapshot requires all snapshot files for the table, and if using incrementalbackups, any incremental backup files created after the snapshot was taken.

Generally, before restoring a snapshot, you should truncate the table. If the backup occurs before thedelete and you restore the backup after the delete without first truncating, you do not get back the originaldata (row). Until compaction, the tombstone is in a different SSTable than the original row, so restoringthe SSTable containing the original row does not remove the tombstone and the data still appears to bedeleted.

Cassandra can only restore data from a snapshot when the table schema exists. If you have not backed upthe schema, you can do the either of the following:

• Method 1

/documentation/cql/3.1/cql/cql_reference/truncate_r.html

/documentation/cql/3.1/cql/cql_reference/delete_r.html


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1. Restore the snapshot, as described below.2. Recreate the schema.

• Method 2

1. Recreate the schema.2. Restore the snapshot, as described below.3. Run nodetool refresh.

Procedure

You can restore a snapshot in several ways:• Use the sstableloader tool.• Copy the snapshot SSTable directory (see Taking a snapshot) to the

data/keyspace/table_name-UUID directory and then call the JMX methodloadNewSSTables() in the column family MBean for each column family through JConsole. You canuse nodetool refresh instead of the loadNewSSTables() call.

The location of the data directory depends on the type of installation:


• Use the Node Restart Method described below.

Node restart method

About this task

If restoring a single node, you must first shutdown the node. If restoring an entire cluster, you must shutdown all nodes, restore the snapshot data, and then start all nodes again.

Note: Restoring from snapshots and incremental backups temporarily causes intensive CPU and I/O activity on the node being restored.

Procedure

1. Shut down the node.

2. Clear all files in the commitlog directory.

• Package installations: /var/lib/cassandra/commitlog• Tarball installations: install_location/data/commitlog

This prevents the commitlog replay from putting data back, which would defeat the purpose of restoringdata to a particular point in time.

3. Delete all *.db files in data_directory_location/keyspace_name/table_name-UUID directory, but DONOT delete the /snapshots and /backups subdirectories.

where data_directory_location is


4. Locate the most recent snapshot folder in this directory:

data_directory_location/keyspace_name/table_name-UUID/snapshots/snapshot_name

5. Copy its contents into this directory:

data_directory_location/keyspace_name/table_name-UUID directory.

6. If using incremental backups, copy all contents of this directory:


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data_directory_location/keyspace_name/table_name-UUID/backups

7. Paste it into this directory:

data_directory_location/keyspace_name/table_name-UUID

8. Restart the node.

Restarting causes a temporary burst of I/O activity and consumes a large amount of CPU resources.

9. Run nodetool repair.

Restoring a snapshot into a new cluster

About this task

Suppose you want to copy a snapshot of SSTable data files from a three node Cassandra cluster withvnodes enabled (256 tokens) and recover it on another newly created three node cluster (256 tokens). Thetoken ranges will not match so you need to specify the tokens for the new cluster that were used in the oldcluster.

Note: This procedure assumes you are familiar with restoring a snapshot and configuring andinitializing a cluster. If not, see Initializing a cluster.

Procedure

To recover the snapshot on the new cluster:

1. From the old cluster, retrieve the list of tokens associated with each node's IP:

$ nodetool ring | grep ip_address_of_node | awk '{print $NF ","}' | xargs

2. In the cassandra.yaml file for each node in the new cluster, add the list of tokens you obtained in theprevious step to the initial_token parameter using the same num_tokens setting as in the old cluster.

3. Make any other necessary changes in the cassandra.yaml and property files so that the new nodesmatch the old cluster settings.

4. Clear the system table data from each new node:


This allows the new nodes to use the initial tokens defined in the cassandra.yaml when they restart.

5. Restore the SSTable files snapshotted from the old cluster onto the new cluster using the samedirectories. Otherwise the new cluster does not have data to read in when you restart the nodes.

6. Start each node using the specified list of token ranges in cassandra.yaml:

initial_token: -9211270970129494930, -9138351317258731895, -8980763462514965928, ...

This allows Cassandra to read the SSTable snapshot from the old cluster.

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Cassandra tools

The nodetool utilityA command line interface for managing a cluster.

Command format

• Package installations: nodetool [(-h <host> | --host <host>)] [(-p <port> | --port<port>)] [(-pwf <passwordFilePath> | --password-file <passwordFilePath>)][(-u <username> | --username <username>)] [(-pw <password> | --password<password>)] <command> [<args>]

• Tarball installations: Execute the command from install_location/bin• If a username and password for RMI authentication are set explicitly in the cassandra-env.sh file for

the host, then you must specify credentials.

The repair and rebuild commands can affect multiple nodes in the cluster.

Most nodetool commands operate on a single node in the cluster if -h is not used to identify one ormore other nodes. If the node from which you issue the command is the intended target, you do notneed the -h option to identify the target; otherwise, for remote invocation, identify the target node, ornodes, using -h.

cfhistogramsProvides statistics about a table that could be used to plot a frequency function.

Synopsis

nodetool <options> cfhistograms -- <keyspace> <table>

• options are:

• ( -h | --host ) <host name> | <ip address>• ( -p | --port ) <port number>• ( -pw | --password ) <password >• ( -u | --username ) <user name>• ( -pwf <passwordFilePath | --password-file <passwordFilePath> )

• -- separates an option from an argument that could be mistaken for a option.• keyspace is the name of a keyspace.• table is the name of a table.

Synopsis Legend

• Angle brackets (< >) mean not literal, a variable• Italics mean optional• The pipe (|) symbol means OR or AND/OR• Ellipsis (...) means repeatable• Orange ( and ) means not literal, indicates scope

Description

The nodetool cfhistograms command provides statistics about a table, including read/write latency,partition size, column count, and number of SSTables. The report covers all operations since the last time

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you ran nodetool cfhistograms in this session. The use of the metrics-core library in Cassandra 2.1 makesthe output more informative and easier to understand.

Example

For example, to get statistics about the libout table in the libdata keyspace on Linux, use this command:

$ install_location/bin/nodetool cfhistograms libdata libout

Output is:

libdata/libout histogramsPercentile SSTables Write Latency Read Latency Partition Size Cell Count (micros) (micros) (bytes) 50% 0.00 39.50 36.00 1597 4275% 0.00 49.00 55.00 1597 4295% 0.00 95.00 82.00 8239 25898% 0.00 126.84 110.42 17084 44699% 0.00 155.13 123.71 24601 770Min 0.00 3.00 3.00 1110 36Max 0.00 50772.00 314.00 126934 3973

The output shows the percentile rank of read and write latency values, the partition size, and the cell countfor the table.

cfstatsProvides statistics about tables.

Synopsis

nodetool <options> cfstats -i -- (<keyspace>.<table> ... ) -H

• options are:


• -- separates an option from an argument that could be mistaken for a option.• i ignores the following tables, providing only information about other Cassandra tables• keyspace.table is one or more keyspace and table names in dot notation.• H converts bytes to a human readable form: kilobytes (KB), megabytes (MB), gigabytes (GB), or

terabytes (TB). (Cassandra 2.1.1)

Synopsis Legend

• Angle brackets (< >) mean not literal, a variable• Italics mean optional• The pipe (|) symbol means OR or AND/OR• Ellipsis (...) means repeatable

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• Orange ( and ) means not literal, indicates scope

Description

The nodetool cfstats command provides statistics about one or more tables. You use dot notationto specify one or more keyspace and table names. If you do not specify a keyspace and table, Cassandraprovides statistics about all tables. If you use the -i option, Cassandra provides statistics about all tablesexcept the given ones. The use of the metrics-core library in Cassandra 2.1 makes the output moreinformative and easier to understand.

This table describes the nodetool cfstats output.

Table 11: nodetool cfstats output

Name ofstatistic

Examplevalue

Briefdescription

Related information

Keyspace libdata Name of thekeyspace

Keyspace and table

Read count 11207 Number ofrequests toread tablesin the libdatakeyspacesince startup

Read latency 0.047. . .ms

Latencyreading thetables inthe libdatakeyspace

OpsCenter alert metrics

Write count 17598 Number ofrequeststo updatetables inthe libdatakeyspacesince startup

Same as above

Write latency 0.053. . .ms

Latencywriting tablesin the libdatakeyspace

Same as above

Pending tasks 0 Tasks in thequeue forreads, writes,and clusteroperations oftables in thekeyspace

OpsCenter pending task metrics

Table libout Name of theCassandratable

SSTable count 3 Number ofSSTables

How to use the SSTable counts metric and OpsCenter alertmetrics


/documentation/opscenter/4.0/opsc/online_help/opscAlertMetrics_r.html

/documentation/opscenter/4.0/opsc/online_help/opscPendingTaskMetrics_r.html



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Name ofstatistic

Examplevalue

Briefdescription

Related information

containingdata from thetable

Space used(live), bytes:

9592399 Space usedby the table(dependson operatingsystem)

Advanced system alert metrics

Space used(total), bytes:

9592399 Same asabove

Same as above

Space usedby snapshots(total), bytes:

0 Sameoccupied bybackup data

SSTablecompressionratio

0.367. . . Fractionof data-representationsize resultingfromcompression

Types of compression option)

Memtable cellcount

1022550 Number ofcells (storageengine rowsx columns)of data in thememtable

Cassandra memtable structure in memory

Memtable datasize, bytes

32028148 Size of thememtabledata

Same as above

Memtable switchcount

3 Number oftimes a fullmemtablewasswappedfor anempty one(Increaseseachtime thememtablefor a tableis flushed todisk)

How memtables are measured article

Local read count 11207 Number oflocal readrequests forthe libouttable sincestartup

OpsCenter alert documentation

/documentation/opscenter/4.0/opsc/online_help/opscAdvancedSystemAlertMetrics_r.html

/documentation/cql/3.1/cql/cql_reference/compressSubprop.html

http://thelastpickle.com/blog/2011/05/04/How-are-Memtables-measured.html


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Name ofstatistic

Examplevalue

Briefdescription

Related information

Local readlatency

0.048 ms Roundtrip time inmillisecondsto completea requestto read thelibout table

Factors that affect read latency

Local writecount

17598 Numberof localrequests toupdate thelibout thetable sincestartup

OpsCenter alert documentation

Local writelatency

0.054 ms Roundtrip time inmillisecondsto completean updateto the libouttable

Factors that affect write latency

Pending tasks 0 Number ofread, write,and clusteroperationsthat arepending

OpsCenter pending task metrics documentation

Bloom filter falsepositives

0 Numberof falsepositives,which occurwhen thebloom filtersaid the rowexisted, butit actuallydid not existin absolutenumbers

Tuning bloom filters

Bloom filter falseratio

0.00000 Fraction ofall bloomfilter checksresulting in afalse positive

Same as above

Bloom filterspace used,bytes

11688 Size of bytesof the bloomfilter data

Same as above


/documentation/opscenter/4.0/opsc/online_help/opscPendingTaskMetrics_r.html

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Name ofstatistic

Examplevalue

Briefdescription

Related information

Compactedpartitionminimum bytes

1110 Lower sizelimit for thepartitionbeingcompacted inmemory

Used to calculate what the approximate row cache sizeshould be. Multiply the reported row cache size, which isthe number of rows in the cache, by the compacted rowmean size for every table and sum them.

Compactedpartitionmaximum bytes

126934 Upper sizelimit forcompactedtable rows.

Configurable in the cassandra.yaml in_memory_compaction_limit_in_mb

Compactedpartition meanbytes

2730 The averagesize ofcompactedtable rows

Averagelive cells perslice (last fiveminutes)

0.0 Averageof cellsscannedby singlekey queriesduring thelast fiveminutes

Averagetombstones perslice (last fiveminutes)

0.0 Average oftombstonesscannedby singlekey queriesduring thelast fiveminutes

Examples

This example shows an excerpt of the output of the command after flushing a table of library data to disk.

nodetool cfstats libdata.liboutKeyspace: libdata Read Count: 11207 Read Latency: 0.047931114482020164 ms. Write Count: 17598 Write Latency: 0.053502954881236506 ms. Pending Flushes: 0 Table: libout SSTable count: 3 Space used (live), bytes: 9088955 Space used (total), bytes: 9088955 Space used by snapshots (total), bytes: 0 SSTable Compression Ratio: 0.36751363892150946 Memtable cell count: 0 Memtable data size, bytes: 0 Memtable switch count: 3 Local read count: 11207 Local read latency: 0.048 ms Local write count: 17598

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Local write latency: 0.054 ms Pending flushes: 0 Bloom filter false positives: 0 Bloom filter false ratio: 0.00000 Bloom filter space used, bytes: 11688 Compacted partition minimum bytes: 1110 Compacted partition maximum bytes: 126934 Compacted partition mean bytes: 2730 Average live cells per slice (last five minutes): 0.0 Average tombstones per slice (last five minutes): 0.0

Using the human-readable option

Using the human-readable -H option (Cassandra 1.1.1) provides output in easier-to-read units than bytes.For example:

nodetool cfstats demodb.nhanes -HKeyspace: demodb Read Count: 0 Read Latency: NaN ms. Write Count: 20050 Write Latency: 0.08548014962593516 ms. Pending Flushes: 0 Table: nhanes SSTable count: 1 Space used (live): 13.75 MB Space used (total): 13.75 MB Space used by snapshots (total): 0 bytes SSTable Compression Ratio: 0.3064650643762481 Memtable cell count: 0 Memtable data size: 0 bytes Memtable switch count: 1 Local read count: 0 Local read latency: NaN ms Local write count: 20050 Local write latency: 0.085 ms Pending flushes: 0 Bloom filter false positives: 0 Bloom filter false ratio: 0.00000 Bloom filter space used: 23.73 KB Compacted partition minimum bytes: 1.87 KB Compacted partition maximum bytes: 2.69 KB Compacted partition mean bytes: 2.26 KB Average live cells per slice (last five minutes): 0.0 Maximum live cells per slice (last five minutes): 0.0 Average tombstones per slice (last five minutes): 0.0 Maximum tombstones per slice (last five minutes): 0.0

----------------

cleanupCleans up keyspaces and partition keys no longer belonging to a node.

Synopsis

nodetool <options> cleanup -- <keyspace> (<table> ...)

• options are:

• ( -h | --host ) <host name> | <ip address>• ( -p | --port ) <port number>• ( -pw | --password ) <password >• ( -u | --username ) <user name>

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• ( -pwf <passwordFilePath | --password-file <passwordFilePath> )• -- separates an option from an argument that could be mistaken for a option.• keyspace is a keyspace name.• table is one or more table names, separated by a space.

Synopsis Legend


Description

Use this command to remove unwanted data after adding a new node to the cluster. Cassandra doesnot automatically remove data from nodes that lose part of their partition range to a newly added node.Run nodetool cleanup on the source node and on neighboring nodes that shared the same subrangeafter the new node is up and running. Failure to run this command after adding a node causes Cassandrato include the old data to rebalance the load on that node. Running the nodetool cleanup commandcauses a temporary increase in disk space usage proportional to the size of your largest SSTable. Disk I/Ooccurs when running this command.

Running this command affects nodes that use a counter column in a table. Cassandra assigns a newcounter ID to the node.

Optionally, this command takes a list of table names. If you do not specify a keyspace, this commandcleans all keyspaces no longer belonging to a node.

clearsnapshotRemoves one or more snapshots.

Synopsis

nodetool <options> clearsnapshot -t <snapshot> -- ( <keyspace> ... )

• options are:


• -t means the following file contains the snapshot.• snapshot is the name of the snapshot.• -- separates an option from an argument that could be mistaken for a option.• keyspace is one or more keyspace names, separated by a space.

Synopsis Legend


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Description

Deletes snapshots in one or more keyspaces. To remove all snapshots, omit the snapshot name.

compactForces a major compaction on one or more tables.

Synopsis

nodetool <options> compact <keyspace> ( <table> ... )

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is the name of a keyspace.• table is one or more table names, separated by a space.

Synopsis Legend


Description

This command starts the compaction process on tables that use the SizeTieredCompactionStrategyand DateTieredCompactionStrategy. You can specify a keyspace for compaction. If you do not specifya keyspace, the nodetool command uses the current keyspace. You can specify one or more tables forcompaction. If you do not specify any tables, compaction of all tables in the keyspace occurs. This is calleda major compaction. If you do specify one or more tables, compaction of the specified tables occurs. Thisis called a minor compaction. A major compaction combines each of the pools of repaired and unrepairedSSTables into one repaired and one unreparied SSTable. During compaction, there is a temporary spike indisk space usage and disk I/O because the old and new SSTables co-exist. A major compaction can causeconsiderable disk I/O.

compactionhistoryProvides the history of compaction operations.

Synopsis

$ nodetool <options> compactionhistory

options are:


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Synopsis Legend


Example

The actual output of compaction history is seven columns wide. The first three columns show the id,keyspace name, and table name of the compacted SSTable.

$ nodetool compactionhistory

Compaction History: id keyspace_name columnfamily_named06f7080-07a5-11e4-9b36-abc3a0ec9088 system schema_columnfamiliesd198ae40-07a5-11e4-9b36-abc3a0ec9088 libdata users0381bc30-07b0-11e4-9b36-abc3a0ec9088 Keyspace1 Standard174eb69b0-0621-11e4-9b36-abc3a0ec9088 system locale35dd980-07ae-11e4-9b36-abc3a0ec9088 system compactions_in_progress8d5cf160-07ae-11e4-9b36-abc3a0ec9088 system compactions_in_progressba376020-07af-11e4-9b36-abc3a0ec9088 Keyspace1 Standard1d18cc760-07a5-11e4-9b36-abc3a0ec9088 libdata libout64009bf0-07a4-11e4-9b36-abc3a0ec9088 libdata liboutd04700f0-07a5-11e4-9b36-abc3a0ec9088 system sstable_activityc2a97370-07a9-11e4-9b36-abc3a0ec9088 libdata userscb928a80-07ae-11e4-9b36-abc3a0ec9088 Keyspace1 Standard1cd8d1540-079e-11e4-9b36-abc3a0ec9088 system schema_columns62ced2b0-07a4-11e4-9b36-abc3a0ec9088 system schema_keyspacesd19cccf0-07a5-11e4-9b36-abc3a0ec9088 system compactions_in_progress640bbf80-07a4-11e4-9b36-abc3a0ec9088 libdata users6cd54e60-07ae-11e4-9b36-abc3a0ec9088 Keyspace1 Standard1c29241f0-07a9-11e4-9b36-abc3a0ec9088 libdata liboutc2a30ad0-07a9-11e4-9b36-abc3a0ec9088 system compactions_in_progresse3a6d920-079d-11e4-9b36-abc3a0ec9088 system schema_keyspaces62c55cd0-07a4-11e4-9b36-abc3a0ec9088 system schema_columnfamilies62b07540-07a4-11e4-9b36-abc3a0ec9088 system schema_columnscdd038c0-079e-11e4-9b36-abc3a0ec9088 system schema_keyspacesb797af00-07af-11e4-9b36-abc3a0ec9088 Keyspace1 Standard18c918b10-07ae-11e4-9b36-abc3a0ec9088 Keyspace1 Standard1377d73f0-07ae-11e4-9b36-abc3a0ec9088 system compactions_in_progress62b9c410-07a4-11e4-9b36-abc3a0ec9088 system locald0566a40-07a5-11e4-9b36-abc3a0ec9088 system schema_columnsba637930-07af-11e4-9b36-abc3a0ec9088 system compactions_in_progresscdbc1480-079e-11e4-9b36-abc3a0ec9088 system schema_columnfamiliese3456f80-07ae-11e4-9b36-abc3a0ec9088 Keyspace1 Standard1d086f020-07a5-11e4-9b36-abc3a0ec9088 system schema_keyspacesd06118a0-07a5-11e4-9b36-abc3a0ec9088 system localcdaafd80-079e-11e4-9b36-abc3a0ec9088 system local640fde30-07a4-11e4-9b36-abc3a0ec9088 system compactions_in_progress

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37638350-07ae-11e4-9b36-abc3a0ec9088 Keyspace1 Standard1

The four columns to the right of the table name show the timestamp, size of the SSTtable before and aftercompaction, and the number of partitions merged. The notation means {tables:rows}. For example: {1:3,3:1} means 3 rows were taken from one SSTable (1:3) and 1 row taken from 3 SSTables (3:1) to make theone SSTable in that compaction operation.

. . . compacted_at bytes_in bytes_out rows_merged

. . . 1404936947592 8096 7211 {1:3, 3:1}

. . . 1404936949540 144 144 {1:1}

. . . 1404941328243 1305838191 1305838191 {1:4647111}

. . . 1404770149323 5864 5701 {4:1}

. . . 1404940844824 573 148 {1:1, 2:2}

. . . 1404940700534 576 155 {1:1, 2:2}

. . . 1404941205282 766331398 766331398 {1:2727158}

. . . 1404936949462 8901649 8901649 {1:9315}

. . . 1404936336175 8900821 8900821 {1:9315}

. . . 1404936947327 223 108 {1:3, 2:1}

. . . 1404938642471 144 144 {1:1}

. . . 1404940804904 383020422 383020422 {1:1363062}

. . . 1404933936276 4889 4177 {1:4}

. . . 1404936334171 441 281 {1:3, 2:1}

. . . 1404936949567 379 79 {2:2}

. . . 1404936336248 144 144 {1:1}

. . . 1404940645958 307520780 307520780 {1:1094380}

. . . 1404938642319 8901649 8901649 {1:9315}

. . . 1404938642429 416 165 {1:3, 2:1}

. . . 1404933543858 692 281 {1:3, 2:1}

. . . 1404936334109 7760 7186 {1:3, 2:1}

. . . 1404936333972 4860 4724 {1:2, 2:1}

. . . 1404933936715 441 281 {1:3, 2:1}

. . . 1404941200880 1269180898 1003196133 {1:2623528, 2:946565}

. . . 1404940699201 297639696 297639696 {1:1059216}

. . . 1404940556463 592 148 {1:2, 2:2}

. . . 1404936334033 5760 5680 {2:1}

. . . 1404936947428 8413 5316 {1:2, 3:1}

. . . 1404941205571 429 42 {2:2}

. . . 1404933936584 7994 6789 {1:4}

. . . 1404940844664 306699417 306699417 {1:1091457}

. . . 1404936947746 601 281 {1:3, 3:1}

. . . 1404936947498 5840 5680 {3:1}

. . . 1404933936472 5861 5680 {3:1}

. . . 1404936336275 378 80 {2:2}

. . . 1404940556293 302170540 281000000 {1:924660, 2:75340}

compactionstatsProvide statistics about a compaction.

Synopsis

nodetool <options> compactionstats -H

• options are:


• -- separates an option and argument that could be mistaken for a option.• data center is the name of an arbitrarily chosen data center from which to select sources for streaming.

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• H converts bytes to a human readable form: kilobytes (KB), megabytes (MB), gigabytes (GB), orterabytes (TB). (Cassandra 2.1.1)

Synopsis Legend


Description

The total column shows the total number of uncompressed bytes of SSTables being compacted. Thesystem log lists the names of the SSTables compacted.

Example

$ bin/nodetool compactionstatspending tasks: 5 compaction type keyspace table completed total unit progress Compaction Keyspace1 Standard1 282310680 302170540 bytes 93.43% Compaction Keyspace1 Standard1 58457931 307520780 bytes 19.01%Active compaction remaining time : 0h00m16s

decommissionDeactivates a node by streaming its data to another node.

Synopsis

nodetool <options> decommission

options are:


Synopsis Legend


DescriptionCauses a live node to decommission itself, streaming its data to the next node on the ring. Use netstats tomonitor the progress, as described on http://wiki.apache.org/cassandra/NodeProbe#Decommission andhttp://wiki.apache.org/cassandra/Operations#Removing_nodes_entirely.

http://wiki.apache.org/cassandra/NodeTool#Decommission

http://wiki.apache.org/cassandra/Operations#Removing_nodes_entirely

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describeclusterProvide the name, snitch, partitioner and schema version of a cluster

Synopsis

nodetool <options> describecluster -- <data center>

• options are:



Synopsis Legend


Description

Describe cluster is typically used to validate the schema after upgrading. If a schema disagreement occurs,check for and resolve schema disagreements.

Example

$ bin/nodetool describeclusterCluster Information: Name: Test Cluster Snitch: org.apache.cassandra.locator.DynamicEndpointSnitch Partitioner: org.apache.cassandra.dht.Murmur3Partitioner Schema versions: 65e78f0e-e81e-30d8-a631-a65dff93bf82: [127.0.0.1]

If a schema disagreement occurs, the last line of the output includes information about unreachable nodes.

$ bin/nodetool describeclusterCluster Information: Name: Production Cluster Snitch: org.apache.cassandra.locator.DynamicEndpointSnitch Partitioner: org.apache.cassandra.dht.Murmur3Partitioner Schema versions: UNREACHABLE: 1176b7ac-8993-395d-85fd-41b89ef49fbb: [10.202.205.203]

describeringProvides the partition ranges of a keyspace.

Synopsis

nodetool <options> describering -- <keyspace>

• options are:

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• -- separates an option from an argument that could be mistaken for a option.• keyspace is a keyspace name.

Synopsis Legend


Example

This example shows the sample output of the command on a three-node cluster.

$ nodetool describering demo_keyspaceSchema Version:1b04bd14-0324-3fc8-8bcb-9256d1e15f82TokenRange: TokenRange(start_token:3074457345618258602, end_token:-9223372036854775808, endpoints:[127.0.0.1, 127.0.0.2, 127.0.0.3], rpc_endpoints:[127.0.0.1, 127.0.0.2, 127.0.0.3], endpoint_details:[EndpointDetails(host:127.0.0.1, datacenter:datacenter1, rack:rack1), EndpointDetails(host:127.0.0.2, datacenter:datacenter1, rack:rack1), EndpointDetails(host:127.0.0.3, datacenter:datacenter1, rack:rack1)]) TokenRange(start_token:-3074457345618258603, end_token:3074457345618258602, endpoints:[127.0.0.3, 127.0.0.1, 127.0.0.2], rpc_endpoints:[127.0.0.3, 127.0.0.1, 127.0.0.2], endpoint_details:[EndpointDetails(host:127.0.0.3, datacenter:datacenter1, rack:rack1), EndpointDetails(host:127.0.0.1, datacenter:datacenter1, rack:rack1), EndpointDetails(host:127.0.0.2, datacenter:datacenter1, rack:rack1)]) TokenRange(start_token:-9223372036854775808, end_token:-3074457345618258603, endpoints:[127.0.0.2, 127.0.0.3, 127.0.0.1], rpc_endpoints:[127.0.0.2, 127.0.0.3, 127.0.0.1], endpoint_details:[EndpointDetails(host:127.0.0.2, datacenter:datacenter1, rack:rack1), EndpointDetails(host:127.0.0.3, datacenter:datacenter1, rack:rack1), EndpointDetails(host:127.0.0.1, datacenter:datacenter1, rack:rack1)])

If a schema disagreement occurs, the last line of the output includes information about unreachable nodes.

$ bin/nodetool describeclusterCluster Information: Name: Production Cluster Snitch: org.apache.cassandra.locator.DynamicEndpointSnitch Partitioner: org.apache.cassandra.dht.Murmur3Partitioner Schema versions: UNREACHABLE: 1176b7ac-8993-395d-85fd-41b89ef49fbb: [10.202.205.203]

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disableautocompactionDisables autocompaction for a keyspace and one or more tables.

Synopsis

nodetool <options> disableautocompaction -- <keyspace> ( <table> ... )

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is the name of a keyspace.• table is one or more table names, separated by a space.

Synopsis Legend


Description

The keyspace can be followed by one or more tables.

disablebackupDisables incremental backup.

Synopsis

nodetool <options> disablebackup

options are:


Synopsis Legend


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disablebinaryDisables the native transport.

Synopsis

nodetool <options> disablebinary

options are:


Synopsis Legend


Description

Disables the binary protocol, also known as the native transport.

disablegossipDisables the gossip protocol.

Synopsis

nodetool <options> disablegossip

options are:


Synopsis Legend


Description

This command effectively marks the node as being down.

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disablehandoffDisables storing of future hints on the current node.

Synopsis

nodetool <options> disablehandoff

options are:


Synopsis Legend


disablethriftDisables the Thrift server.

Synopsis

nodetool <options> disablethrift

options are:


Synopsis Legend


drainDrains the node.

Synopsis

nodetool <options> drain

options are:

• ( -h | --host ) <host name> | <ip address>• ( -p | --port ) <port number>

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• ( -pw | --password ) <password >• ( -u | --username ) <user name>• ( -pwf <passwordFilePath | --password-file <passwordFilePath> )

Synopsis Legend


Description

Flushes all memtables from the node to SSTables on disk. Cassandra stops listening for connections fromthe client and other nodes. You need to restart Cassandra after running nodetool drain. You typicallyuse this command before upgrading a node to a new version of Cassandra. To simply flush memtables todisk, use nodetool flush.

enableautocompactionEnables autocompaction for a keyspace and one or more tables.

Synopsis

nodetool <options> enableautocompaction -- <keyspace> ( <table> ... )

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is the name of a keyspace.• table is the name of one or more keyspaces, separated by a space.

Synopsis Legend


DescriptionThe keyspace can be followed by one or more tables. Enables compaction for the named keyspace or thecurrent keyspace, and one or more named tables, or all tables.

enablebackupEnables incremental backup.

Synopsis

nodetool <options> enablebackup

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options are:


Synopsis Legend


enablebinaryRe-enables native transport.

Synopsis

nodetool <options> enablebinary

options are:


Synopsis Legend


Description

Re-enables the binary protocol, also known as native transport.

enablegossipRe-enables gossip.

Synopsis

nodetool <options> enablegossip

options are:


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Synopsis Legend


enablehandoffRe-enables the storing of future hints on the current node.

Synopsis

nodetool <options> enablehandoff

options are:


Synopsis Legend


enablethriftRe-enables the Thrift server.

Synopsis

nodetool <options> enablethrift

options are:


Synopsis Legend


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flushFlushes one or more tables from the memtable.

Synopsis

nodetool <options> flush -- <keyspace> ( <table> ... )

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is the name of a keyspace.• table is the name of one or more tables, separated by a space.

Synopsis Legend


Description

You can specify a keyspace followed by one or more tables that you want to flush from the memtable toSSTables on disk.

getcompactionthresholdProvides the minimum and maximum compaction thresholds in megabytes for a table.

Synopsis

nodetool <options> getcompactionthreshold -- <keyspace> <table>

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is the name of a keyspace.• table is the name of a table.

Synopsis Legend


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getendpointsProvides the IP addresses or names of replicas that own the partition key.

Synopsis

nodetool <options> getendpoints -- <keyspace> <table> key

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is a keyspace name.• table is a table name.• key is the partition key of the end points you want to get.

Synopsis Legend


Example

For example, which nodes own partition key_1, key_2, and key_3?

$ bin/nodetool -h 127.0.0.1 -p 7100 getendpoints myks mytable key_1127.0.0.2$ bin/nodetool -h 127.0.0.1 -p 7100 getendpoints myks mytable key_2127.0.0.2$ bin/nodetool -h 127.0.0.1 -p 7100 getendpoints myks mytable key_3127.0.0.1

getlogginglevelsGet the runtime logging levels.

Synopsis

nodetool <options> getlogginglevels

options are:

• ( -h | --host ) <host name> | <ip address>• ( -p | --port ) <port number>• ( -pw | --password ) <password>• ( -u | --username ) <user name>• ( -pwf <passwordFilePath | --password-file <passwordFilePath> )

Synopsis Legend

• Angle brackets (< >) mean not literal, a variable• Italics mean optional• The pipe (|) symbol means OR or AND/OR

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• Ellipsis (...) means repeatable• Orange ( and ) means not literal, indicates scope

getsstablesProvides the SSTables that own the partition key.

Synopsis

nodetool <options> getsstables -- <keyspace> <table> key

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is a keyspace name.• table is a table name.• key is the partition key of the SSTables.

Synopsis Legend


getstreamthroughputProvides the megabytes per second throughput limit for streaming in the system.

Synopsis

nodetool <options> getstreamthroughput

options are:


Synopsis Legend


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gossipinfoProvides the gossip information for the cluster.

Synopsis

nodetool <options> gossipinfo

options are:


Synopsis Legend


helpProvides nodetool command help.

Synopsis

nodetool help <command>

Synopsis Legend


Description

Using this command without the The help command provides a synopsis and brief description of eachnodetool command.

Examples

Using nodetool help lists all commands and usage information. For example, nodetool help netstatsprovides the following information.

NAME nodetool netstats - Print network information on provided host (connecting node by default)

SYNOPSIS nodetool [(-h <host> | --host <host>)] [(-p <port> | --port <port>)] [(-pw <password> | --password <password>)] [(-u <username> | --username <username>)] netstats

OPTIONS

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-h <host>, --host <host> Node hostname or ip address

-p <port>, --port <port> Remote jmx agent port number

-pw <password>, --password <password> Remote jmx agent password

-u <username>, --username <username> Remote jmx agent username

infoProvides node information, such as load and uptime.

Synopsis

nodetool <options> info ( -T | --tokens )

• options are:


• -T or --tokens means provide all token information.

Synopsis Legend


Description

Provides node information including the token and on disk storage (load) information, times started(generation), uptime in seconds, and heap memory usage.

invalidatekeycacheResets the global key cache parameter to the default, which saves all keys.

Synopsis

nodetool <options> invalidatekeycache

options are:


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Synopsis Legend


DescriptionBy default the key_cache_keys_to_save is disabled in the cassandra.yaml. This command resets theparameter to the default.

invalidaterowcacheResets the global key cache parameter, row_cache_keys_to_save, to the default (not set), which saves allkeys.

Synopsis

nodetool <options> invalidaterowcache

options are:


Synopsis Legend


joinCauses the node to join the ring.

Synopsis

nodetool <options> join

options are:


Synopsis Legend

• Angle brackets (< >) mean not literal, a variable• Italics mean optional• The pipe (|) symbol means OR or AND/OR

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• Ellipsis (...) means repeatable• Orange ( and ) means not literal, indicates scope

Description

Causes the node to join the ring, assuming the node was initially not started in the ring using the -Djoin_ring=false cassandra utility option. The joining node should be properly configured with the desiredoptions for seed list, initial token, and auto-bootstrapping.

listsnapshotsLists snapshot names, size on disk, and true size.

Synopsis

nodetool <options> listsnapshots

options are:


Synopsis Legend


Description

Available in Cassandra 2.1 and later.

Example

Snapshot Details: Snapshot Name Keyspace Column Family True Size Size on Disk

1387304478196 Keyspace1 Standard1 0 bytes 308.66 MB1387304417755 Keyspace1 Standard1 0 bytes 107.21 MB1387305820866 Keyspace1 Standard2 0 bytes 41.69 MB Keyspace1 Standard1 0 bytes 308.66 MB

moveMoves the node on the token ring to a new token.

Synopsis

nodetool <options> move -- <new token>

• options are:

• ( -h | --host ) <host name> | <ip address>• ( -p | --port ) <port number>• ( -pw | --password ) <password >

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• ( -u | --username ) <user name>• ( -pwf <passwordFilePath | --password-file <passwordFilePath> )

• -- separates an option and argument that could be mistaken for a option.• new token is a number in the range 0 to 2127 -1 for negative tokens.

Synopsis Legend


Description

Escape negative tokens using \\ . For example: move \\-123 . This command essentially combinesdecommission and bootstrapoperations.

netstatsProvides network information about the host.

Synopsis

nodetool <options> netstats -H

• options are:


• H converts bytes to a human readable form: kilobytes (KB), megabytes (MB), gigabytes (GB), orterabytes (TB). (Cassandra 2.1.1)

Synopsis Legend


Description

The default host is the connected host if the user does not include a host name or IP address in thecommand. The output includes the following information:

• JVM settings• Mode• Read repair statistics• Attempted

The number of successfully completed read repair operations• Mismatch (blocking)

The number of read repair operations since server restart that blocked a query.

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• Mismatch (background)

The number of read repair operations since server restart performed in the background.• Pool name

Information about client read and write requests by thread pool.• Active, pending, and completed number of commands and responses

Example

Get the network information for a node 10.171.147.128:

nodetool -h 10.171.147.128 netstats

The output is:

Mode: NORMALNot sending any streams.Read Repair Statistics:Attempted: 0Mismatch (Blocking): 0Mismatch (Background): 0Pool Name Active Pending CompletedCommands n/a 0 1156Responses n/a 0 2750

pausehandoffPauses the hints delivery process

Synopsis

nodetool <options> pausehandoff

options are:


Synopsis Legend


proxyhistogramsProvides a histogram of network statistics.

Synopsis

nodetool <options> proxyhistograms

options are:

• ( -h | --host ) <host name> | <ip address>• ( -p | --port ) <port number>• ( -pw | --password ) <password >

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• ( -u | --username ) <user name>• ( -pwf <passwordFilePath | --password-file <passwordFilePath> )

Synopsis Legend


Description

The output of this command shows the full request latency recorded by the coordinator. The outputincludes the percentile rank of read and write latency values for inter-node communication. Typically, youuse the command to see if requests encounter a slow node.

ExamplesThis example shows the output from nodetool proxyhistograms after running 4,500 insert statements and45,000 select statements on a three ccm node-cluster on a local computer.

$ nodetool proxyhistogramsproxy histogramsPercentile Read Latency Write Latency Range Latency (micros) (micros) (micros)50% 1502.50 375.00 446.0075% 1714.75 420.00 498.0095% 31210.25 507.00 800.2098% 36365.00 577.36 948.4099% 36365.00 740.60 1024.39Min 616.00 230.00 311.00Max 36365.00 55726.00 59247.00

rangekeysampleProvides the sampled keys held across all keyspaces.

Synopsis

nodetool <options> rangekeysample

options are:


Synopsis Legend


https://github.com/pcmanus/ccm

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rebuildRebuilds data by streaming from other nodes.

Synopsis

nodetool <options> rebuild -- <data center>

• options are:



Synopsis Legend


Description

This command operates on multiple nodes in a cluster. Similar to bootstrap. Rebuild (like bootstrap) onlystreams data from a single source replica per range. Use this command to bring up a new data center in anexisting cluster.

rebuild_indexPerforms a full rebuild of the index for a table

Synopsis

nodetool <options> rebuild_index -- <keyspace> <table>( <index> ... )

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is a keyspace name.• table is a table name.• index is an optional list of index names separated by a space.

Synopsis Legend


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Description

Fully rebuilds one or more indexes for a table.

refreshLoads newly placed SSTables onto the system without a restart.

Synopsis

nodetool <options> refresh -- <keyspace> <table>

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is a keyspace name.• table is a table name.

Synopsis Legend


reloadtriggersReloads trigger classes.

Synopsis

nodetool <options> reloadtriggers

options are:


Synopsis Legend


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DescriptionAvailable in Cassandra 2.1 and later.

removenodeProvides the status of current node removal, forces completion of pending removal, or removes theidentified node.

Synopsis

nodetool <options> removenode -- <status> | <force> | <ID>

• options are:


• -- separates an option and argument that could be mistaken for a option.• status provides status information.• force forces completion of the pending removal.• ID is the host ID, in UUID format.

Synopsis Legend


DescriptionThis command removes a node, shows the status of a removal operation, or forces the completionof a pending removal. When the node is down and nodetool decommission cannot be used, usenodetool removenode. Run this command only on nodes that are down. If the cluster does not usevnodes, before running the nodetool removenode command, adjust the tokens.

Examples

Determine the UUID of the node to remove by running nodetool status. Use the UUID of the node thatis down to remove the node.

$ nodetool status

Datacenter: DC1===============Status=Up/Down|/ State=Normal/Leaving/Joining/Moving-- Address Load Tokens Owns (effective) Host ID RackUN 192.168.2.101 112.82 KB 256 31.7% 420129fc-0d84-42b0-be41-ef7dd3a8ad06 RAC1DN 192.168.2.103 91.11 KB 256 33.9% d0844a21-3698-4883-ab66-9e2fd5150edd RAC1UN 192.168.2.102 124.42 KB 256 32.6% 8d5ed9f4-7764-4dbd-bad8-43fddce94b7c RAC1

$ nodetool removenode d0844a21-3698-4883-ab66-9e2fd5150edd

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View the status of the operation to remove the node:

$ nodetool removenode status RemovalStatus: No token removals in process.

Confirm that the node has been removed.

$ nodetool status

Datacenter: DC1===============Status=Up/Down|/ State=Normal/Leaving/Joining/Moving-- Address Load Tokens Owns (effective) Host ID RackUN 192.168.2.101 112.82 KB 256 37.7% 420129fc-0d84-42b0-be41-ef7dd3a8ad06 RAC1UN 192.168.2.102 124.42 KB 256 38.3% 8d5ed9f4-7764-4dbd-bad8-43fddce94b7c RAC1

repairRepairs one or more tables.

Synopsis

nodetool <options> repair ( -dc <dc_name> ) | ( --in-dc <dc_name> ) ( -et <end_token>) | ( --end-token <end_token> ) ( -hosts <host_name host_name . . . > ) | ( --in-hosts <host_name host_name . . .> ) ( -inc | --incremental ) ( -local | --in-local-dc ) ( -par | --parallel ) ( -pr | --partitioner-range ) ( -st <start_token> ) | ( --start-token <start_token> ) -- <keyspace> ( <table> ... )

• options are:


• -dc, or --in-dc, followed by dc_name, or means restrict repair to nodes in the named data center, whichmust be the local data center.

• -et, or --end-token, followed by the UUID of a token means means stop repairing a range of nodes afterrepairing this token. Use -hosts to specify neighbor nodes.

• -hosts <host_name host_name . . . >, or --in-hosts <host_name host_name . . .>. Used to reducenetwork traffic.

• -inc, or --incremental means do an incremental repair.• -local, or --in-local-dc, means repair nodes in the same data center only.• -par, or --parallel, means do a parallel repair.• -pr, or --partitioner-range, means repair only the first range returned by the partitioner.• -st, or --start-token, followed by the UUID of a token means start repairing a range of nodes at this

token.• -- separates an option and argument that could be mistaken for a option.• keyspace is the keyspace name. The default is all.• table is one or more table names, separated by a space. The default is all.

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Synopsis Legend


Description

Performing an anti-entropy node repair on a regular basis is important, especially when frequently deletingdata. The nodetool repair command repairs one or more nodes in a cluster, and includes an option torestrict repair to a set of nodes. Anti-entropy node repair performs the following tasks:

• Ensures that all data on a replica is consistent.• Repairs inconsistencies on a node that has been down.

By default, Cassandra 2.1 does a full, sequential repair.

Using options

You can use options to do these other types of repair:

• Incremental• Parallel

Use the -hosts option to list the good nodes to use for repairing the bad nodes. Use -h to name the badnodes.

Use the -inc option for an incremental repair. An incremental repair eliminates the need for constant Merkletree construction by persisting already repaired data and calculating only the Merkle trees for SSTablesthat have not been repaired. The repair process is likely more performant than the other types of repaireven as datasets grow, assuming you run repairs frequently. Before doing an incremental repair for the firsttime, perform migration steps first if necessary.

Use the -par option for a parallel repair. Unlike sequential repair, parallel repair constructs the Merkletables for all nodes at the same time. Therfore, no snapshots are required (or generated). Use a parallelrepair to complete the repair quickly or when you have operational downtime that allows the resources tobe completely consumed during the repair.

Performing partitioner range repairs by using the -pr option is generally not recommended.

Example

All nodetool repair arguments are optional. The following examples show the following types of repair:

• An incremental, parallel repair of all keyspaces on the current node• A partitioner range repair of the bad partition on current node using the good partitions on 10.2.2.20 or

10.2.2.21• A start-point-to-end-point repair of all nodes between two nodes on the ring

$ nodetool repair -par -inc$ nodetool repair -pr -hosts 10.2.2.20 10.2.2.21$ nodetool -st a9fa31c7-f3c0-44d1-b8e7-a26228867840c -et f5bb146c-db51-475ca44f-9facf2f1ad6e

To restrict the repair to the local data center, use the -dc option followed by the name of the data center.Issue the command from a node in the data center you want to repair. Issuing the command from a datacenter other than the named one returns an error.

$ nodetool repair -dc DC1[2014-07-24 21:59:55,326] Nothing to repair for keyspace 'system'

http://www.datastax.com/dev/blog/more-efficient-repairs

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[2014-07-24 21:59:55,617] Starting repair command #2, repairing 490 ranges for keyspace system_traces (seq=true, full=true)[2014-07-24 22:23:14,299] Repair session 323b9490-137e-11e4-88e3-c972e09793ca for range (820981369067266915,822627736366088177] finished[2014-07-24 22:23:14,320] Repair session 38496a61-137e-11e4-88e3-c972e09793ca for range (2506042417712465541,2515941262699962473] finished. . .

An inspection of the system.log shows repair taking place only on IP addresses in DC1.

. . .INFO [AntiEntropyStage:1] 2014-07-24 22:23:10,708 RepairSession.java:171 - [repair #16499ef0-1381-11e4-88e3-c972e09793ca] Received merkle tree for sessions from /192.168.2.101INFO [RepairJobTask:1] 2014-07-24 22:23:10,740 RepairJob.java:145 - [repair #16499ef0-1381-11e4-88e3-c972e09793ca] requesting merkle trees for events (to [/192.168.2.103, /192.168.2.101]). . .

resetlocalschemaReset the node's local schema and resynchronizes.

Synopsis

nodetool <options> resetlocalschema

options are:


Synopsis Legend


resumehandoffResume hints delivery process.

Synopsis

nodetool <options> resumehandoff

options are:


Synopsis Legend

• Angle brackets (< >) mean not literal, a variable

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• Italics mean optional• The pipe (|) symbol means OR or AND/OR• Ellipsis (...) means repeatable• Orange ( and ) means not literal, indicates scope

ringProvides node status and information about the ring.

Synopsis

nodetool <options> ring ( -r | --resolve-ip ) -- <keyspace>

• options are:


• -r, or --resolve-ip, means to provide node names instead of IP addresses.• -- separates an option and argument that could be mistaken for a option.• keyspace is a keyspace name.

Synopsis Legend


Description

Displays node status and information about the ring as determined by the node being queried. Thisinformation can give you an idea of the load balance and if any nodes are down. If your cluster is notproperly configured, different nodes may show a different ring. Check that the node appears the same wayin the ring.If you use virtual nodes (vnodes), use nodetool status for succinct output.

• Address

The node's URL.• DC (data center)

The data center containing the node.• Rack

The rack or, in the case of Amazon EC2, the availability zone of the node.• Status - Up or Down

Indicates whether the node is functioning or not.• State - N (normal), L (leaving), J (joining), M (moving)

The state of the node in relation to the cluster.• Load - updates every 90 seconds

The amount of file system data under the cassandra data directory after excluding all content in thesnapshots subdirectories. Because all SSTable data files are included, any data that is not cleaned up,such as TTL-expired cell or tombstoned data) is counted.

• Token

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The end of the token range up to and including the value listed. For an explanation of token ranges, seeData Distribution in the Ring .

• Owns

The percentage of the data owned by the node per data center times the replication factor. Forexample, a node can own 33% of the ring, but show100% if the replication factor is 3.

• Host ID

The network ID of the node.

scrubRebuild SSTables for one or more Cassandra tables.

Synopsis

nodetool <options> scrub <keyspace> -- ( -ns | --no-snapshot ) ( -s | --skip-corrupted ) ( <table> ... )

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is the name of a keyspace.• -ns, or --no-snapshot, triggers a snapshot of the scrubbed table first assuming snapshots are not

disabled (the default).• - s, or --skip-corrupted skips corrupted partitions even when scrubbing counter tables. (default false)• table is one or more table names, separated by a space.

Synopsis Legend


DescriptionRebuilds SSTables on a node for the named tables and snapshots data files before rebuilding as a safetymeasure. If possible use upgradesstables. While scrub rebuilds SSTables, it also discards data that itdeems broken and creates a snapshot, which you have to remove manually. If the -ns option is specified,snapshot creation is disabled. If scrub can't validate the column value against the column definition's datatype, it logs the partition key and skips to the next partition. Skipping corrupted partitions in tables havingcounter columns results in under-counting. By default the scrub operation stops if you attempt to skip sucha partition. To force the scrub to skip the partition and continue scrubbing, re-run nodetool scrub usingthe --skip-corrupted option.

http://www.datastax.com/docs/1.1/cluster_architecture/partitioning#data-distribution-in-the-ring

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setcachecapacitySet global key and row cache capacities in megabytes.

Synopsis

nodetool <options> setcachecapacity -- <key-cache-capacity> <row-cache-capacity>

• options are:


• -- separates an option and argument that could be mistaken for a option.• key-cache-capacity is the maximum size in MB of the key cache in memory.• row-cache-capacity corresponds to the maximum size in MB of the row cache in memory.

Synopsis Legend


DescriptionThe key-cache-capacity argument corresponds to the key_cache_size_in_mb parameter in thecassandra.yaml. Each key cache hit saves one seek and each row cache hit saves a minimum of twoseeks. Devoting some memory to the key cache is usually a good tradeoff considering the positive effecton the response time. The default value is empty, which means a minimum of five percent of the heap inMB or 100 MB.

The row-cache-capacity argument corresponds to the row_cache_size_in_mb parameter in thecassandra.yaml. By default, row caching is zero (disabled).

setcachekeystosaveSets the number of keys saved by each cache for faster post-restart warmup.

Synopsis

nodetool <options> setcachekeystosave -- <key-cache-keys-to-save> <row-cache-keys-to-save>

• options are:


• -- separates an option and argument that could be mistaken for a option.• key-cache-keys-to-save is the number of keys from the key cache to save to the saved caches

directory.• row-cache-keys-to-save is the number of keys from the row cache to save to the saved caches

directory.

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Synopsis Legend


Description

This command saves the specified number of key and row caches to the saved caches directory,which you specify in the cassandra.yaml. The key-cache-keys-to-save argument corresponds to thekey_cache_keys_to_save in the cassandra.yaml, which is disabled by default, meaning all keys willbe saved. The row-cache-keys-to-save argument corresponds to the row_cache_keys_to_save in thecassandra.yaml, which is disabled by default.

setcompactionthresholdSets minimum and maximum compaction thresholds for a table.

Synopsis

nodetool <options> setcompactionthreshold -- <keyspace> <table> <minthreshold> <maxthreshold>

• options are:


• -- separates an option and argument that could be mistaken for a option.• keyspace is the name of a keyspace.• table is a table name.• minthreshold sets the minimum number of SSTables to trigger a minor compaction when using

SizeTieredCompactionStrategy or DateTieredCompactionStrategy.• maxthreshold sets the maximum number of SSTables to allow in a minor compaction when using

SizeTieredCompactionStrategy or DateTieredCompactionStrategy.

Synopsis Legend


DescriptionThis parameter controls how many SSTables of a similar size must be present before a minor compactionis scheduled. The max_threshold table property sets an upper bound on the number of SSTables thatmay be compacted in a single minor compaction, as described in http://wiki.apache.org/cassandra/MemtableSSTable.

When using LeveledCompactionStrategy, maxthreshold sets the MAX_COMPACTING_L0, which limitsthe number of L0 SSTables that are compacted concurrently to avoid wasting memory or running out ofmemory when compacting highly overlapping SSTables.

/documentation/cql/3.1/cql/cql_reference/compactSubprop.html

http://wiki.apache.org/cassandra/MemtableSSTable

http://wiki.apache.org/cassandra/MemtableSSTable

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setcompactionthroughputSets the throughput capacity for compaction in the system, or disables throttling.

Synopsis

nodetool <options> setcompactionthroughput -- <value_in_mb>

• options are:


• -- separates an option and argument that could be mistaken for a option.• value_in_mb is the throughput capacity in MB per second for compaction.

Synopsis Legend


Description

Set value_in_mb to 0 to disable throttling.

sethintedhandoffthrottlekbSets hinted handoff throttle in kb/sec per delivery thread. (Cassandra 2.1.1 and later)

Synopsis

nodetool <options> sethintedhandoffthrottlekb <value_in_kb/sec>

• options are:


• value_in_kb/sec is the throttle time.

Synopsis Legend


Description

When a node detects that a node for which it is holding hints has recovered, it begins sending the hints tothat node. This setting specifies the maximum sleep interval per delivery thread in kilobytes per second

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after delivering each hint. The interval shrinks proportionally to the number of nodes in the cluster. Forexample, if there are two nodes in the cluster, each delivery thread uses the maximum interval; if there arethree nodes, each node throttles to half of the maximum interval, because the two nodes are expected todeliver hints simultaneously.

Example

nodetool sethintedhandoffthrottlekb 2048

setlogginglevelSet the log level for a service.

Synopsis

nodetool <options> setlogginglevel -- < class_qualifier > < level >

options are:

• ( -h | --host ) <host name> | <ip address>• ( -p | --port ) <port number>• ( -pw | --password ) <password>• ( -u | --username ) <user name>• ( -pwf <passwordFilePath | --password-file <passwordFilePath> )• -- separates an option and argument that could be mistaken for a option.• class_qualifier is the logger class qualifier, a fully qualified domain name, such as

org.apache.cassandra.service.StorageProxy.• level is the logging level, for example DEBUG.

Synopsis Legend


Description

You can use this command to set logging levels for services instead of modifying the logback-text.xml file.The following values are valid for the logger class qualifier:

• org.apache.cassandra• org.apache.cassandra.db• org.apache.cassandra.service.StorageProxy

The possible log levels are:

• ALL• TRACE• DEBUG• INFO• WARN• ERROR• OFF

If both class qualifer and level arguments to the command are empty or null, the command resets loggingto the initial configuration.

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Example

This command sets the StorageProxy service to debug level.

nodetool setlogginglevel org.apache.cassandra.service.StorageProxy DEBUG

setstreamthroughputSets the throughput capacity in MB for streaming in the system, or disable throttling.

Synopsis

nodetool <options> setstreamthroughput -- <value_in_mb>

• options are:


• -- separates an option and argument that could be mistaken for a option.• value_in_mb is the throughput capacity in MB per second for streaming.

Synopsis Legend


DescriptionSet value_in_MB to 0 to disable throttling.

settraceprobabilitySets the probability for tracing a request.

Synopsis

nodetool <options> settraceprobability -- <value>

• options are:


• -- separates an option and argument that could be mistaken for a option.• value is a probability between 0 and 1.

Synopsis Legend


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DescriptionProbabilistic tracing is useful to determine the cause of intermittent query performance problems byidentifying which queries are responsible. This option traces some or all statements sent to a cluster.Tracing a request usually requires at least 10 rows to be inserted.

A probability of 1.0 will trace everything whereas lesser amounts (for example, 0.10) only sample a certainpercentage of statements. Care should be taken on large and active systems, as system-wide tracingwill have a performance impact. Unless you are under very light load, tracing all requests (probability1.0) will probably overwhelm your system. Start with a small fraction, for example, 0.001 and increaseonly if necessary. The trace information is stored in a system_traces keyspace that holds two tables –sessions and events, which can be easily queried to answer questions, such as what the most time-consuming query has been since a trace was started. Query the parameters map and thread column in thesystem_traces.sessions and events tables for probabilistic tracing information.

snapshotTake a snapshot of one or more keyspaces, or of a table, to backup data.

Synopsis

nodetool <options> snapshot ( -cf <table> | --column-family <table> ) ( -t <tag> | --tag <tag> ) -- ( <keyspace> ) | ( <keyspace> ... )

• options are:


• -cf, or --column-family, followed by the name of the table to be backed up.• -t or --tag, followed by the snapshot name.• -- separates an option and argument that could be mistaken for a option.• keyspace is a single keyspace name that is required when using the -cf option• keyspace_list is one or more optional keyspace names, separated by a space.

Synopsis Legend


DescriptionUse this command to back up data using a snapshot. Depending on how you use the command, thefollowing data is included:

• All keyspaces on a node.

Omit the optional keyspace and table parameters, as shown in the first example.• One or more keyspaces and all tables in the named keyspaces.

Include one or more names of the keyspaces, as shown in the second and third examples.

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• A single table.

Include the name of a single keyspace and a table using the -cf option, as shown in the last example.

Cassandra flushes the node before taking a snapshot, takes the snapshot, and stores the data in thesnapshots directory of each keyspace in the data directory. If you do not specify the name of a snapshotdirectory using the -t option, Cassandra names the directory using the timestamp of the snapshot, forexample 1391460334889. Follow the procedure for taking a snapshot before upgrading Cassandra. Whenupgrading, backup all keyspaces. For more information about snapshots, see Apache documentation.

Example: All keyspaces

Take a snapshot of all keyspaces on the node. On Linux, in the Cassandra bin directory, for example:

$ bin/nodetool snapshot

The following message appears:

Requested creating snapshot(s) for [all keyspaces] with snapshot name [1391464041163]Snapshot directory: 1391464041163

Because you did not specify a snapshot name, Cassandra names snapshot directories using thetimestamp of the snapshot. If the keyspace contains no data, empty directories are not created.

Example: Single keyspace snapshot

Assuming you created the keyspace and tables in the music service example, take a snapshot of the musickeyspace and name the snapshot 2014.06.24. On Linux, in the Cassandra bin directory, for example:

$ bin/nodetool snapshot -t 2014.06.24 music


Requested creating snapshot(s) for [music] with snapshot name [2014.06.24]Snapshot directory: 2014.06.24

Assuming the music keyspace contains two tables, songs and playlists, taking a snapshot of the keyspacecreates multiple snapshot directories named 2014.06.24. A number of .db files containing the data arelocated in these directories. For example, from the installation directory:

$ cd data/data/music/playlists-bf8118508cfd11e3972273ded3cb6170/snapshots/1404936753154$ lsmusic-playlists-ka-1-CompressionInfo.db music-playlists-ka-1-Index.db music-playlists-ka-1-TOC.txtmusic-playlists-ka-1-Data.db music-playlists-ka-1-Statistics.dbmusic-playlists-ka-1-Filter.db music-playlists-ka-1-Summary.db$ cd data/data/music/songs-b8e385a08cfd11e3972273ded3cb6170/2014.06.24/snapshots/1404936753154music-songs-ka-1-CompressionInfo.db music-songs-ka-1-Index.db music-songs-ka-1-TOC.txtmusic-songs-ka-1-Data.db music-songs-ka-1-Statistics.dbmusic-songs-ka-1-Filter.db music-songs-ka-1-Summary.db

Example: Multiple keyspaces snapshot

Assuming you created a keyspace named mykeyspace in addition to the music keyspace, take a snapshotof both keyspaces. On Linux, in the Cassandra bin directory, for example:

$ bin/nodetool snapshot mykeyspace music


Requested creating snapshot(s) for [mykeyspace, music] with snapshot name [1391460334889]Snapshot directory: 1391460334889

http://wiki.apache.org/cassandra/Operations#Backing_up_data


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Example: Single table snapshot

Take a snapshot of only the playlists table in the music keyspace. On Linux, in the Cassandra bindirectory, for example:

$ bin/nodetool snapshot -cf playlists musicRequested creating snapshot(s) for [music] with snapshot name [1391461910600]Snapshot directory: 1391461910600

Cassandra creates the snapshot directory named 1391461910600 that contains the backup data ofplaylists table in data/data/music/playlists-bf8118508cfd11e3972273ded3cb6170/snapshots, for example.

statusProvide information about the cluster, such as the state, load, and IDs.

Synopsis

nodetool <options> status ( -r | --resolve-ip ) -- <keyspace>

• options are:


• -r, or --resolve-ip, means to provide node names instead of IP addresses.• -- separates an option and argument that could be mistaken for a option.• keyspace is a keyspace name.

Synopsis Legend


Description

The status command provides the following information:

• Status - U (up) or D (down)

Indicates whether the node is functioning or not.• State - N (normal), L (leaving), J (joining), M (moving)

The state of the node in relation to the cluster.• Address

The node's URL.• Load - updates every 90 seconds

The amount of file system data under the cassandra data directory after excluding all content in thesnapshots subdirectories. Because all SSTable data files are included, any data that is not cleaned up,such as TTL-expired cell or tombstoned data) is counted.

• Tokens

The number of tokens set for the node.

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• Owns

The percentage of the data owned by the node per data center times the replication factor. Forexample, a node can own 33% of the ring, but show 100% if the replication factor is 3.

Attention: If your cluster uses keyspaces having different replication strategies or replicationfactors, specify a keyspace when you run nodetool status to get meaningful ownshipinformation.

• Host ID

The network ID of the node.• Rack

The rack or, in the case of Amazon EC2, the availability zone of the node.

Example

This example shows the output from running nodetool status.

nodetool status mykeyspace

Datacenter: datacenter1=======================Status=Up/Down|/ State=Normal/Leaving/Joining/Moving-- Address Load Tokens Owns Host ID RackUN 127.0.0.1 47.66 KB 1 33.3% aaa1b7c1-6049-4a08-ad3e-3697a0e30e10 rack1UN 127.0.0.2 47.67 KB 1 33.3% 1848c369-4306-4874-afdf-5c1e95b8732e rack1UN 127.0.0.3 47.67 KB 1 33.3% 49578bf1-728f-438d-b1c1-d8dd644b6f7f rack1

statusbinaryProvide the status of native transport.

Synopsis

nodetool <options> statusbinary

options are:


Synopsis Legend


DescriptionProvides the status of the binary protocol, also known as the native transport.

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statusthriftProvide the status of the Thrift server.

Synopsis

nodetool <options> statusthrift

options are:


Synopsis Legend


stopStops the compaction process.

Synopsis

nodetool <options> stop -- <compaction_type>

• options are:


• -- separates an option and argument that could be mistaken for a option.• A compaction type: COMPACTION, VALIDATION, CLEANUP, SCRUB, INDEX_BUILD

Synopsis Legend


Description

Stops an operation from continuing to run. This command is typically used to stop a compaction that has anegative impact on the performance of a node. After the compaction stops, Cassandra continues with theremaining operations in the queue. Eventually, Cassandra restarts the compaction.

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stopdaemonStops the cassandra daemon.

Synopsis

nodetool <options> stopdaemon

options are:


Synopsis Legend


tpstatsProvides usage statistics of thread pools.

Synopsis

nodetool <options> tpstats

options are:


Synopsis Legend


Description

Run the nodetool tpstats command on the local node. The nodetool tpstats command provides statisticsabout the number of active, pending, and completed tasks for each stage of Cassandra operations bythread pool. A high number of pending tasks for any pool can indicate performance problems, as describedin http://wiki.apache.org/cassandra/Operations#Monitoring.

This table describes key indicators:

http://wiki.apache.org/cassandra/Operations#Monitoring

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Table 12: nodetool tpstats output

Name of statistic Task Related information

CounterMutationStage Local counter changes

ReadStage Local reads

RequestResponseStage Handle responses from othernodes

MutationStage Local writes A high number of pending writerequests indicates a problemhandling them. Tune hardware orCassandra configuration.

ReadRepairStage A digest query and update ofreplicas of a key

GossipStage Handle gossip rounds everysecond

CacheCleanupExecutor Clears the cache

AntiEntropyStage Repair consistency Nodetool repair

MigrationStage Make schema changes

ValidationExecutor Validates schema

CommitlogArchiver Archives commitlog

MiscStage Miscellaneous operations

MemtableFlushWriter Writes memtable contents todisk

MemtableReclaimMemory Makes unused memoryavailable

PendingRangeCalculator Calculate pending rangesper bootstraps and departednodes

Developer notes

MemtablePostFlush

CompactionExecutor Runs compaction

InternalResponseStage Respond to non-clientinitiated messages, includingbootstrapping and schemachecking

HintedHandoff Send missed mutations toother nodes

Example

Run the command every two seconds.

nodetool -h labcluster tpstats

Example output is:

Pool Name Active Pending Completed Blocked All time blocked

http://wiki.apache.org/cassandra/DigestQueries

https://issues.apache.org/jira/secure/attachment/12564093/5135-v2.txt

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CounterMutationStage 0 0 0 0 0ReadStage 0 0 103 0 0RequestResponseStage 0 0 0 0 0MutationStage 0 0 13234794 0 0ReadRepairStage 0 0 0 0 0GossipStage 0 0 0 0 0CacheCleanupExecutor 0 0 0 0 0AntiEntropyStage 0 0 0 0 0MigrationStage 0 0 11 0 0ValidationExecutor 0 0 0 0 0CommitLogArchiver 0 0 0 0 0MiscStage 0 0 0 0 0MemtableFlushWriter 0 0 126 0 0MemtableReclaimMemory 0 0 126 0 0PendingRangeCalculator 0 0 1 0 0MemtablePostFlush 0 0 1468 0 0CompactionExecutor 0 0 254 0 0InternalResponseStage 0 0 1 0 0HintedHandoff 0 0 0

Message type DroppedRANGE_SLICE 0READ_REPAIR 0PAGED_RANGE 0BINARY 0READ 0MUTATION 180_TRACE 0REQUEST_RESPONSE 0COUNTER_MUTATION 0

truncatehintsTruncates all hints on the local node, or truncates hints for the one or more endpoints.

Synopsis

nodetool <options> truncatehints -- ( <endpoint> ... )

• options are:

• ( -h | --host ) <host name> | <ip address>• ( -p | --port ) <port number>• ( -pw | --password ) <password >• ( -u | --username ) <user name>

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• ( -pwf <passwordFilePath | --password-file <passwordFilePath> )• -- separates an option and argument that could be mistaken for a option.• endpoint is one or more endpoint IP addresses or host names which hints are to be deleted.

Synopsis Legend


upgradesstablesRewrites SSTables for tables that are not running the current version of Cassandra.

Synopsis

nodetool <options> upgradesstables ( -a | --include-all-sstables ) -- <keyspace> ( <table> ... )

• options are:


• -a or --include-all-sstables, followed by the snapshot name.• -- separates an option and argument that could be mistaken for a option.• keyspace a keyspace name.• table is one or more table names, separated by a space.

Synopsis Legend


DescriptionRewrites SSTables on a node that are incompatible with the current version. Use this command whenupgrading your server or changing compression options.

versionProvides the version number of Cassandra running on the specified node.

Synopsis

nodetool <options> version

options are:

• ( -h | --host ) <host name> | <ip address>• ( -p | --port ) <port number>

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• ( -pw | --password ) <password >• ( -u | --username ) <user name>• ( -pwf <passwordFilePath | --password-file <passwordFilePath> )

Synopsis Legend


Cassandra bulk loader (sstableloader)

About this task

The Cassandra bulk loader, also called the sstableloader, provides the ability to:

• Bulk load external data into a cluster.• Load existing SSTables into another cluster with a different number of nodes or replication strategy.• Restore snapshots.

The sstableloader streams a set of SSTable data files to a live cluster; it does not simply copy the setof SSTables to every node, but transfers the relevant part of the data to each node, conforming to thereplication strategy of the cluster. The table into which the data is loaded does not need to be empty.

If tables are repaired in a different cluster, after being loaded, the tables will be unrepaired.

Prerequisites

Because sstableloader uses Cassandra gossip, make sure of the following:

• The cassandra.yaml configuration file is in the classpath and properly configured.• At least one node in the cluster is configured as seed.• In the cassandra.yaml file, the following properties are properly configured for the cluster that you

are importing into:

• cluster_name• listen_address• storage_port• rpc_address• rpc_port

When using sstableloader to load external data, you must first generate SSTables.

If using DataStax Enterprise, you can use Sqoop to migrate external data to Cassandra.

Generating SSTables

SSTableWriter is the API to create raw Cassandra data files locally for bulk load into your cluster. TheCassandra source code includes the CQLSSTableWriter implementation for creating SSTable files fromexternal data without needing to understand the details of how those map to the underlying storage engine.Import the org.apache.cassandra.io.sstable.CQLSSTableWriter class, and define the schemafor the data you want to import, a writer for the schema, and a prepared insert statement, as shown inCassandra 2.0.1, 2.0.2, and a quick peek at 2.0.3.

Using sstableloader

Before loading the data, you must define the schema of the tables with CQL or Thrift.

/documentation/datastax_enterprise/4.6/datastax_enterprise/ana/anaSqpAbt.html

http://www.datastax.com/dev/blog/cassandra-2-0-1-2-0-2-and-a-quick-peek-at-2-0-3

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To get the best throughput from SSTable loading, you can use multiple instances of sstableloader tostream across multiple machines. No hard limit exists on the number of SSTables that sstableloader canrun at the same time, so you can add additional loaders until you see no further improvement.

If you use sstableloader on the same machine as the Cassandra node, you can't use the same networkinterface as the Cassandra node. However, you can use the JMX StorageService > bulkload() call fromthat node. This method takes the absolute path to the directory where the SSTables are located, andloads them just as sstableloader does. However, because the node is both source and destination for thestreaming, it increases the load on that node. This means that you should load data from machines that arenot Cassandra nodes when loading into a live cluster.

Usage:


$ sstableloader [options] path_to_keyspace


$ cd install_location/bin$ sstableloader [options] path_to_keyspace

The sstableloader bulk loads the SSTables found in the keyspace directory to the configured target cluster,where the parent directories of the directory path are used as the target keyspace/table name.

1. Go to the location of the SSTables:

$ cd /var/lib/cassandra/data/Keyspace1/Standard1/2. To view the contents of the keyspace:

$ ls

Keyspace1-Standard1-jb-60-CRC.dbKeyspace1-Standard1-jb-60-Data.db...Keyspace1-Standard1-jb-60-TOC.txt

3. To bulk load the files, specify the path to Keyspace1/Standard1/ in the target cluster:

$ sstableloader -d 110.82.155.1 /var/lib/cassandra/data/Keyspace1/Standard1/ ## package installation

$ install_location/bin/sstableloader -d 110.82.155.1 /var/lib/cassandra/data/Keyspace1/Standard1/ ## tarball installation

This bulk loads all files.

Table 13: sstableloader options

Short option Long option Description

-alg --ssl-alg<ALGORITHM>

Client SSL algorithm (default: SunX509).

-ciphers --ssl-ciphers <CIPHER-SUITES>

Client SSL. Comma-separated list of encryption suites.

-cph --connections-per-host<connectionsPerHost>

Number of concurrent connections-per-host.

-d --nodes <initial_hosts> Required. Connect to a list of (comma separated) hosts forinitial cluster information.

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Short option Long option Description

-f --conf-path<path_to_config_file>

Path to the cassandra.yaml path for streamingthroughput and client/server SSL.

-h --help Display help.

-i --ignore <NODES> Do not stream to this comma separated list of nodes.

-ks --keystore<KEYSTORE>

Client SSL. Full path to the keystore.

-kspw --keystore-password<KEYSTORE-PASSWORD>

Client SSL. Password for the keystore.

--no-progress Do not display progress.

-p --port <rpc port> RPC port (default: 9160 [Thift]).

-prtcl --ssl-protocol<PROTOCOL>

Client SSL. Connections protocol to use (default: TLS).

-pw --password<password>

Password for Cassandra authentication.

-st --store-type <STORE-TYPE>

Client SSL. Type of store.

-t --throttle <throttle> Throttle speed in Mbits (default: unlimited).

-tf --transport-factory<transport factory>

Fully-qualified ITransportFactory class name forcreating a connection to Cassandra.

-ts --truststore<TRUSTSTORE>

Client SSL. Full path to truststore.

-tspw --truststore-password<TRUSTSTORE-PASSWORD>

Client SSL. Password of the truststore.

-u --username<username>

User name for Cassandra authentication.

-v --verbose Verbose output.

The following cassandra.yaml options can be over-ridden from the command line:

Option in cassandra.yaml Command line example

stream_throughput_outbound_megabits_per_sec --throttle 300

server_encryption_options --ssl-protocol none

client_encryption_options --keystore-password MyPassword

The cassandra utility

About this task

Cassandra start-up parameters can be run from the command line (in Tarball installations) or specified inthe cassandra-env.sh file (Package or Tarball installations).

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File locations

cassandra-env.sh

• Tarball installations: install_location/conf/cassandra-env.sh• Package installations: /etc/cassandra/cassandra-env.sh

You can also use the cassandra-env.sh file to pass additional options, such as maximum and minimumheap size, to the Java virtual machine rather than setting them in the environment.

Usage

Add the following to the cassandra-env.sh file:

JVM_OPTS="$JVM_OPTS -D[PARAMETER]"

For Tarball installations, you can run this tool from the command line:

cassandra [OPTIONS]

Examples:

• cassandra-env.sh: JVM_OPTS="$JVM_OPTS -Dcassandra.load_ring_state=false"• Command line: bin/cassandra -Dcassandra.load_ring_state=false

The Example section contains more examples.

Command line only options

Option Description

-f Start the cassandra process in foreground. The default is to start as backgroundprocess.

-h Help.

-p filename Log the process ID in the named file. Useful for stopping Cassandra by killing its PID.

-v Print the version and exit.

Start-up parameters

The -D option specifies the start-up parameters in both the command line and cassandra-env.sh file.

cassandra.auto_bootstrap=false

Facilitates setting auto_bootstrap to false on initial set-up of the cluster. The next time you start the cluster,you do not need to change the cassandra.yaml file on each node to revert to true.

cassandra.available_processors=number_of_processors

In a multi-instance deployment, multiple Cassandra instances will independently assume that all CPUprocessors are available to it. This setting allows you to specify a smaller set of processors.

cassandra.boot_without_jna=true

If JNA fails to initialize, Cassandra fails to boot. Use this command to boot Cassandra without JNA.

cassandra.config=directory

The directory location of the cassandra.yaml file. The default location depends on the type of installation.

cassandra.initial_token=token

Use when virtual nodes (vnodes) are not used. Sets the initial partitioner token for a node the first time thenode is started. (Default: disabled)

Note: Vnodes are highly recommended as they automatically select tokens.

cassandra.join_ring=true|false

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Set to false to start Cassandra on a node but not have the node join the cluster. (Default: true) You can usenodetool join and a JMX call to join the ring afterwards.

cassandra.load_ring_state=true|false

Set to false to clear all gossip state for the node on restart. (Default: true)

cassandra.metricsReporterConfigFile=file

Enable pluggable metrics reporter. See Pluggable metrics reporting in Cassandra 2.0.2.

cassandra.native_transport_port=port

Set the port on which the CQL native transport listens for clients. (Default: 9042)

cassandra.partitioner=partitioner

Set the partitioner. (Default: org.apache.cassandra.dht.Murmur3Partitioner)

cassandra.replace_address=listen_address or broadcast_address of dead node

To replace a node that has died, restart a new node in its place specifying the listen_address orbroadcast_address that the new node is assuming. The new node must not have any data in its datadirectory, that is, it must be in the same state as before bootstrapping.

Note: The broadcast_address defaults to the listen_address except when using theEC2MultiRegionSnitch.

cassandra.replayList=table

Allow restoring specific tables from an archived commit log.

cassandra.ring_delay_ms=ms

Defines the amount of time a node waits to hear from other nodes before formally joining the ring. (Default:1000ms)

cassandra.rpc_port=port

Set the port for the Thrift RPC service, which is used for client connections. (Default: 9160).

cassandra.ssl_storage_port=port

Set the SSL port for encrypted communication. (Default: 7001)

cassandra.start_native_transport=true|false

Enable or disable the native transport server. See start_native_transport in cassandra.yaml. (Default:true)

cassandra.start_rpc=true/false

Enable or disable the Thrift RPC server. (Default: true)

cassandra.storage_port=port

Set the port for inter-node communication. (Default: 7000)

cassandra.triggers_dir=directory

Set the default location for the trigger JARs. (Default: conf/triggers)

cassandra.write_survey=true

For testing new compaction and compression strategies. It allows you to experiment with different strategiesand benchmark write performance differences without affecting the production workload. See Testingcompaction and compression.

consistent.rangemovement=true

True makes Cassandra 2.1 bootstrapping behavior effective. False makes Cassandra 2.0 behavior effective.

Example

Clear gossip state when starting a node:

• Command line: bin/cassandra -Dcassandra.load_ring_state=false• cassandra-env.sh: JVM_OPTS="$JVM_OPTS -Dcassandra.load_ring_state=false"

Start Cassandra on a node and do not join the cluster:

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• Command line: bin/cassandra -Dcassandra.join_ring=false• cassandra-env.sh: JVM_OPTS="$JVM_OPTS -Dcassandra.join_ring=false"

Replacing a dead node:

• Command line: bin/cassandra -Dcassandra.replace_address=10.91.176.160• cassandra-env.sh: JVM_OPTS="$JVM_OPTS -Dcassandra.replace_address=10.91.176.160"

The cassandra-stress toolA Java-based stress testing utility for basic benchmarking and load testing a Cassandra cluster.

About this task

The choices you make when data modeling your application can make a big difference in how yourapplication performs. Creating the best data model requires significant load testing and multiple iterations.The cassandra-stress tool helps you in this endeavor by populating your cluster and supporting stresstesting of arbitrary CQL tables and arbitrary queries on tables. Use the cassandra-stress tool to:

• Quickly determine how a schema performs.• Understand how your database scales.• Optimize your data model and settings.• Determine production capacity.

Note: You can also use this tool on Cassandra 2.0 clusters.

The cassandra-stress tool also supports a YAML-based profile for defining specific schema with potentialcompaction strategies, cache settings, and types. Sample files are located in:

• Package installations: /usr/share/doc/cassandra/examples• Tarball installations: install_location/tools

For a complete description on using these sample files, see Improved Cassandra 2.1 Stress Tool:Benchmark Any Schema – Part 1.

The cassandra-stress tool creates a keyspace called Keyspace1 and within that, tables named Standard1,Counter1, depending on what type of table is being tested. These are automatically created the first timeyou run the stress test and are reused on subsequent runs unless you drop the keyspace using CQL. Youcannot change the names; they are hard-coded.

Usage:

• Package installations: cassandra-stress command [options]• Tarball installations: install_location/tools/bin/cassandra-stress command

[options]

On tarball installations, you can use these commands and options with or without the cassandra-stressdaemon running.

Command Description

read Multiple concurrent reads. The cluster must first be populated by a write test.

write Multiple concurrent writes against the cluster.

mixed Interleave basic commands with configurable ratio and distribution. The clustermust first be populated by a write test.

counter_write Multiple concurrent updates of counters.

http://www.datastax.com/dev/blog/improved-cassandra-2-1-stress-tool-benchmark-any-schema

http://www.datastax.com/dev/blog/improved-cassandra-2-1-stress-tool-benchmark-any-schema

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Command Description

counter_read Multiple concurrent reads of counters. The cluster must first be populated by acounter_write test.

user Interleave user provided queries with configurable ratio and distribution.

help Display help for a command or option.Display help for an option: cassandra-stress help [options] Forexample: cassandra-stress help -schema

print Inspect the output of a distribution definition.

legacy Legacy support mode.

Important: Additional sub options are available for each option in the following table. See Viewschema help for an example.

Option Description

-pop Population distribution and intra-partition visit order.

-insert Insert specific options relating to various methods for batching and splittingpartition updates.

-col Column details, such as size and count distribution, data generator, names,and comparator.

-rate Thread count, rate limit, or automatic mode (default is auto).

-mode Thrift or CQL with options.

-schema Replication settings, compression, compaction, and so on.

-node Nodes to connect to.

-log Where to log progress and the interval to use.

-transport Custom transport factories.

-port Specify port for connecting Cassandra nodes.

-sendto Specify stress server to send this command to.

View schema help

$ cassandra-stress help -schema

replication([strategy=?][factor=?][<option 1..N>=?]): Define the replication strategy and any parameters strategy=? (default=org.apache.cassandra.locator.SimpleStrategy) The replication strategy to use factor=? (default=1) The number of replicaskeyspace=? (default=Keyspace1) The keyspace name to usecompaction([strategy=?][<option 1..N>=?]): Define the compaction strategy and any parameters strategy=? The compaction strategy to use

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compression=? Specify the compression to use for SSTable, default:no compression

Populate the database

Generally it is easier to let cassandra-stress create the basic schema and then modify it in CQL:

#Load one row with default schema$ cassandra-stress write n=1 cl=one -mode native cql3 -log file=~/create_schema.log #Modify schema in CQL$ cqlsh #Run a real write workload$ cassandra-stress write n=1000000 cl=one -mode native cql3 -schema keyspace="Keyspace1" -log file=~/load_1M_rows.log

Running a mixed workload

When running a mixed workload, you must escape parentheses, greater-than and less-than signs, andother such things. This example invokes a workload that is one-quarter writes and three-quarters reads.

$ cassandra-stress mixed ratio$write=1,read=3$ n=100000 cl=ONE -pop dist=UNIFORM$1..1000000$ -schema keyspace="Keyspace1" -mode native cql3 -rate threads\>=16 threads\<=256 -log file=~/mixed_autorate_50r50w_1M.log

Notice the following in this example:

1. The ratio requires backslash-escaped parenthesis.2. The value of n is different than in write phase. During the write phase, n records are written. However in

the read phase, if n is too large, it is inconvenient to read all the records for simple testing. Generally, ndoes not need be large when validating the persistent storage systems of a cluster.

The -pop dist=UNIFORM$1..1000000$ portion says that of the n=100,000 operations, select thekeys uniformly distributed between 1 and 1,000,000. Use this when you want to specify more data pernode than what fits in DRAM.

3. In the rate section, the greater-than and less-than signs are escaped. If not escaped, the shell willattempt to use them for IO redirection. Specifically, the shell will try to read from a non-existent filecalled =256 and create a file called =16. The rate section tells cassandra-stress to automaticallyattempt different numbers of client threads and not test less that 16 or more than 256 client threads.

Standard mixed read/write workload keyspace for a single node

CREATE KEYSPACE "Keyspace1" WITH replication = { 'class': 'SimpleStrategy', 'replication_factor': '1'};USE "Keyspace1";CREATE TABLE "Standard1" ( key blob, "C0" blob, "C1" blob, "C2" blob, "C3" blob, "C4" blob, PRIMARY KEY (key)) WITH


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bloom_filter_fp_chance=0.010000 AND caching='KEYS_ONLY' AND comment='' AND dclocal_read_repair_chance=0.000000 AND gc_grace_seconds=864000 AND index_interval=128 AND read_repair_chance=0.100000 AND replicate_on_write='true' AND default_time_to_live=0 AND speculative_retry='99.0PERCENTILE' AND memtable_flush_period_in_ms=0 AND compaction={'class': 'SizeTieredCompactionStrategy'} AND compression={'sstable_compression': 'LZ4Compressor'};

Splitting up a load over multiple cassandra-stress instances on different nodes

This example is useful for loading into large clusters, where a single cassandra-stress load generator nodecannot saturate the cluster. In this example, $NODES is a variable whose value is a comma delimited list ofIP addresses such as 10.0.0.1,10.0.0.2, and so on.

#On Node1$ cassandra-stress write n=1000000 cl=one -mode native cql3 -schema keyspace="Keyspace1" -pop seq=1..1000000 -log file=~/node1_load.log -node $NODES #On Node2$ cassandra-stress write n=1000000 cl=one -mode native cql3 -schema keyspace="Keyspace1" -pop seq=1000001..2000000 -log file=~/node2_load.log -node $NODES

Note the keyspace is defined and the -key option tells each instance which range of keys to populate.

Using the Daemon ModeThe daemon in larger-scale testing can prevent potential skews in the test results by keeping the JVMwarm.

The daemon is only available in tarball installations. Run the daemon from:

install_location/tools/bin/cassandra-stressd start|stop|status [-h <host>]

During stress testing, you can keep the daemon running and send it commands through it using the --send-to option.

Example

• Insert 1,000,000 rows to given host:

/tools/bin/cassandra-stress -d 192.168.1.101

When the number of rows is not specified, one million rows are inserted.• Read 1,000,000 rows from given host:

tools/bin/cassandra-stress -d 192.168.1.101 -o read• Insert 10,000,000 rows across two nodes:

/tools/bin/cassandra-stress -d 192.168.1.101,192.168.1.102 -n 10000000• Insert 10,000,000 rows across two nodes using the daemon mode:

/tools/bin/cassandra-stress -d 192.168.1.101,192.168.1.102 -n 10000000 --send-to 54.0.0.1

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Interpreting the output of cassandra-stressAbout the period output from the running tests.

Each line reports data for the interval between the last elapsed time and current elapsed time.

Created keyspaces. Sleeping 1s for propagation.total,interval_op_rate,interval_key_rate,latency,95th,99.9th,elapsed_time19523,1227,1227,41.6,86.1,189.1,2141348,2182,2182,22.5,75.7,176.0,31...END

Table 14: Output of cassandra-stress

Data Description

total Total number of operations since the start of the test.

interval_op_rate Number of operations per second performed during the interval.

interval_key_rate Number of keys/rows read or written per second during the interval (normallybe the same as interval_op_rate unless doing range slices).

latency Average latency in milliseconds for each operation during that interval.

95th 95% of the time the latency was less than the number displayed in thecolumn (Cassandra 1.2 or later).

99.9th 99.9% of the time the latency was less than the number displayed in thecolumn (Cassandra 1.2 or later).

elapsed_time Number of seconds elapsed since the beginning of the test.

The sstablescrub utility

About this task

The sstablescrub utility is an offline version of nodetool scrub. It attempts to remove the corrupted partswhile preserving non-corrupted data.

Before using sstablescrub, try rebuilding the tables using nodetool scrub. If nodetool scrub does not fix theproblem, use this utility. Because it runs offline, sstablescrub can correct errors that nodetool scrub cannot.After running this utility, you must perform a repair because corrupted rows are thrown away.

If scrubbing results in dropping rows, new SSTables become unrepaired, however, if no bad rows aredetected, the SSTable keeps its original repairedAt field, which denotes the time of the repair.

Usage:

• Package installations: sstablescrub [options] <keyspace> <table>• Tarball installations: install_location/bin/sstablescrub [options] <keyspace>

<table>

Table 15: Options

Flag Option Description

--debug Display stack traces.


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-m --manifest-check Only check and repair the leveled manifest, without actually scrubbing theSSTables.

-s --skip-corrupted Skip corrupt rows in counter tables.


The sstablesplit utilityUse this tool to split SSTables files into multiple SSTables of a maximum designated size.

Cassandra must be stopped to use this tool:


$ sudo service cassandra stop• Tarball installations:


Usage:

• Package installations: sstablessplit [options] <filename> [<filename>]*• Tarball installations: install_location/tools/bin/sstablessplit [options]

<filename> [<filename>]*

Example:

$ sstablesplit -s 40 /var/lib/cassandra/data/Keyspace1/Standard1/*

Table 16: Options




--no-snapshot Do not snapshot the SSTables before splitting.

-s --size <size> Maximum size in MB for the output SSTables (default: 50).


The sstablekeys utilityThe sstablekeys utility dumps table keys.

About this task

To list the keys in an SSTable, find the name of the SSTable file. The file is located in the data directoryand has a .db extension. The location of the data directory, listed in the "Install locations" section,depends on the type of installation. After finding the name of the file, use the name as an argument to thesstablekeys command.

$ bin/sstablekeys <sstable_name>

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Procedure

1. Create the playlists table in the music keyspace as shown in Data modeling.

2. Insert the row of data about ZZ Top in playlists:

INSERT INTO music.playlists (id, song_order, song_id, title, artist, album) VALUES (62c36092-82a1-3a00-93d1-46196ee77204, 1, a3e64f8f-bd44-4f28-b8d9-6938726e34d4, 'La Grange', 'ZZ Top', 'Tres Hombres');

3. Flush the data to disk.

$ nodetool flush music playlists

4. Look at keys in the SSTable data. For example, use sstablekeys followed by the path to the data. Usethe path to data for your Cassandra installation:

$ sstablekeys <path to data>/data/data/music/ playlists-8b9f4cc0229211e4b02073ded3cb6170/music-playlists-ka-1-Data.db

The output appears, for example:

62c3609282a13a0093d146196ee77204

The sstableupgrade toolUpgrade the SSTables in the specified table (or snapshot) to match the current version of Cassandra.

About this task

This tool rewrites the SSTables in the specified table to match the currently installed version of Cassandra.

If restoring with sstableloader, you must upgrade your snapshots before restoring for any snapshot taken ina major version older than the major version that Cassandra is currently running.

Usage:

• Package installations: sstableupgrade [options] <keyspace> <cf> [snapshot]• Tarball installations: install_location/bin/sstableupgrade [options] <keyspace>

<cf> [snapshot]

The snapshot option only upgrades the specified snapshot.

Table 17: Options





/documentation/cql/3.1/cql/cql_reference/insert_r.html

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References

Starting and stopping Cassandra

Starting Cassandra as a serviceStart the Cassandra Java server process for packaged installations.

About this task

Startup scripts are provided in /etc/init.d. The service runs as the cassandra user.

Procedure

You must have root or sudo permissions to start Cassandra as a service.

On initial start-up, each node must be started one at a time, starting with your seed nodes:


On Enterprise Linux systems, the Cassandra service runs as a java process.

Starting Cassandra as a stand-alone processStart the Cassandra Java server process for tarball installations.

Procedure

On initial start-up, each node must be started one at a time, starting with your seed nodes.• To start Cassandra in the background:


• To start Cassandra in the foreground:

$ cd install_location$ bin/cassandra -f

Stopping Cassandra as a serviceStop the Cassandra Java server process on packaged installations.

Procedure

You must have root or sudo permissions to stop the Cassandra service:

$ sudo service cassandra stop

Stopping Cassandra as a stand-alone processStop the Cassandra Java server process on tarball installations.

Procedure

Find the Cassandra Java process ID (PID), and then kill the process using its PID number:

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Clearing the data as a serviceRemove all data from a package installation.

Procedure

To clear the data from the default directories:

After stopping the service, run the following command:

$ sudo rm -rf /var/lib/cassandra/*

Clearing the data as a stand-alone processRemove all data from a tarball installation.

Procedure

To clear all data from the default directories, including the commitlog and saved_caches:

1. After stopping the process, run the following command from the install directory:

$ cd install_location$ sudo rm -rf data/*

2. To clear the only the data directory:

$ cd install_location$ sudo rm -rf data/data/*

Install locations

Tarball installation directories

The configuration files are located in the following directories:

Configuration Files Locations

cassandra.yaml install_location/conf

cassandra-topology.properties install_location/conf

cassandra-rackdc.properties install_location/conf

cassandra-env.sh install_location/conf

cassandra.in.sh install_location/bin

The binary tarball releases install into the installation directory.

Directories Description

data Files for commitlog, data, and saved_caches(unless set in cassandra.yaml)

bin Utilities and start scripts

conf Configuration files and environment settings

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interface Thrift and Avro client APIs

javadoc Cassandra Java API documentation

lib JAR and license files

tools Cassandra tools and sample cassandra.yaml filesfor stress testing.

For DataStax Enterprise installs, see the documentation for your DataStax Enterprise version.

Package installation directories

The configuration files are located in the following directories:

Configuration Files Locations

cassandra.yaml /etc/cassandra

cassandra-topology.properties /etc/cassandra

cassandra-rackdc.properties /etc/cassandra

cassandra-env.sh /etc/cassandra

cassandra.in.sh /usr/share/cassandra

The packaged releases install into these directories:


/var/lib/cassandra

Data directories

/var/log/cassandra

Log directory

/var/run/cassandra

Runtime files

/usr/share/cassandra

Environment settings

/usr/share/cassandra/lib

JAR files

/usr/bin Optional utilities, such as sstablelevelreset, sstablerepairedset, and sstablesplit

/usr/bin Binary files

/usr/sbin

/etc/cassandra Configuration files

/etc/init.d Service startup script

/etc/security/limits.d

Cassandra user limits

/etc/default

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/usr/share/doc/cassandra/examples

Sample cassandra.yaml files for stress testing.

For DataStax Enterprise installs, see the documentation for your DataStax Enterprise version.

Cassandra include file

To set environment variables (Linux only), Cassandra can use an include file, cassandra.in.sh. Thisfile is located in:

• Tarball installations: install_location/bin/cassandra.in.sh• Package installations: /usr/share/cassandra/cassandra.in.sh

Cassandra-CLI utility (deprecated)

Important: The CLI utility is deprecated and will be removed in Cassandra 3.0. For ease of useand performance, switch from Thrift and CLI to CQL and cqlsh.

Keyspace attributes

Cassandra stores storage configuration attributes in the system keyspace. You can set storage engineconfiguration attributes on a per-keyspace or per-table basis on the command line using the Cassandra-CLI utility. A keyspace must have a user-defined name, a replica placement strategy, and options thatspecify the number of copies per data center or node.

name

Required. The name for the keyspace.

placement_strategy

Required. Determines how Cassandra distributes replicas for a keyspace among nodes in the ring. Valuesare:

• SimpleStrategy or org.apache.cassandra.locator.SimpleStrategy• NetworkTopologyStrategy or

org.apache.cassandra.locator.NetworkTopologyStrategy

NetworkTopologyStrategy requires a snitch to be able to determine rack and data center locations of a node.For more information about replication placement strategy, see Data replication.

strategy_options

Specifies configuration options for the chosen replication strategy class. The replication factor option is thetotal number of replicas across the cluster. A replication factor of 1 means that there is only one copy ofeach row on one node. A replication factor of 2 means there are two copies of each row, where each copyis on a different node. All replicas are equally important; there is no primary or master replica. As a generalrule, the replication factor should not exceed the number of nodes in the cluster. However, you can increasethe replication factor and then add the desired number of nodes.

When the replication factor exceeds the number of nodes, writes are rejected, but reads are served as longas the desired consistency level can be met.

For more information about configuring the replication placement strategy for a cluster and data centers,see Choosing keyspace replication options.

durable_writes


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(Default: true) When set to false, data written to the keyspace bypasses the commit log. Be careful usingthis option because you risk losing data.

Table attributes

The following attributes can be declared per table.

bloom_filter_fp_chance

See CQL properties in CQL for Cassandra 2.x.

bucket_high

See CQL Compaction Subproperties in CQL for Cassandra 2.x.

bucket_low


caching


chunk_length_kb

See CQLCompression Subproperties in CQL for Cassandra 2.x.

column_metadata

(Default: N/A - container attribute) Column metadata defines these attributes of a column:

• name: Binds a validation_class and (optionally) an index to a column.• validation_class: Type used to check the column value.• index_name: Name of the index.• index_type: Type of index. Currently the only supported value is KEYS.

Setting a value for the name option is required. The validation_class is set to the default_validation_classof the table if you do not set the validation_class option explicitly. The value of index_type must be set tocreate an index for a column. The value of index_name is not valid unless index_type is also set.

Setting and updating column metadata with the Cassandra-CLI utility requires a slightly different commandsyntax than other attributes; note the brackets and curly braces in this example:

[default@demo ] UPDATE COLUMN FAMILY users WITH comparator =UTF8TypeAND column_metadata =[{column_name: full_name, validation_class: UTF8Type, index_type: KEYS }];

column_type

(Default: Standard) The standard type of table contains regular columns.

comment


compaction_strategy

See compaction in CQL properties in CQL for Cassandra 2.x.

compaction_strategy_options

(Default: N/A - container attribute) Sets attributes related to the chosen compaction-strategy. Attributes are:

• bucket_high• bucket_low• max_compaction_threshold• min_compaction_threshold• min_sstable_size• sstable_size_in_mb• tombstone_compaction_interval• tombstone_threshold

/documentation/cql/3.1/cql/cql_reference/tabProp.html#tabProp__table_cql_properties

/documentation/cql/3.1/cql/cql_reference/compactSubprop.html#compactSubprop__compactionSubproperties



/documentation/cql/3.1/cql/cql_reference/compressSubprop.html#compressSubprop__table_compression



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comparator

(Default: BytesType) Defines the data types used to validate and sort column names. There are severalbuilt-in column comparators available. The comparator cannot be changed after you create a table.

compression_options

(Default: N/A - container attribute) Sets the compression algorithm and sub-properties for the table. Choicesare:

• sstable_compression• chunk_length_kb• crc_check_chance

crc_check_chance

See CQLCompression Subproperties in CQL for Cassandra 2.x.

default_time_to_live


default_validation_class

(Default: N/A) Defines the data type used to validate column values. There are several built-in columnvalidators available.

gc_grace


index_interval


key_validation_class

(Default: N/A) Defines the data type used to validate row key values. There are several built-in key validatorsavailable, however CounterColumnType (distributed counters) cannot be used as a row key validator.

max_compaction_threshold

See max_threshold in CQL Compaction Subproperties in CQL for Cassandra 2.x.

min_compaction_threshold

See min_threshold in CQL Compaction Subproperties in CQL for Cassandra 2.x.

max_index_interval


min_index_interval


memtable_flush_after_mins

Deprecated as of Cassandra 1.0, but can still be declared for backward compatibility. Usecommitlog_total_space_in_mb.

memtable_flush_period_in_ms


memtable_operations_in_millions


memtable_throughput_in_mb


min_sstable_size


name

(Default: N/A) Required. The user-defined name of the table.

/documentation/cql/3.1/cql/cql_reference/compressSubprop.html#compressSubprop__table_compression










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read_repair_chance


speculative_retry


sstable_size_in_mb


sstable_compression

See compression in CQL properties in CQL for Cassandra 2.x.

tombstone_compaction_interval


tombstone_threshold








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Moving data to or from other databases

Cassandra offers several solutions for migrating from other databases:

• The COPY command, which mirrors what the PostgreSQL RDBMS uses for file/export import.• The Cassandra bulk loader provides the ability to bulk load external data into a cluster.

About the COPY command

You can use COPY in Cassandra’s CQL shell to load flat file data into Cassandra (nearly all RDBMS’shave unload utilities that allow table data to be written to OS files) as well as data to be written out to OSfiles.

ETL Tools

If you need more sophistication applied to a data movement situation (more than just extract-load), thenyou can use any number of extract-transform-load (ETL) solutions that now support Cassandra. Thesetools provide excellent transformation routines that allow you to manipulate source data in literally any wayyou need and then load it into a Cassandra target. They also supply many other features such as visual,point-and-click interfaces, scheduling engines, and more.

Many ETL vendors who support Cassandra supply community editions of their products that are freeand able to solve many different use cases. Enterprise editions are also available that supply many othercompelling features that serious enterprise data users need.

You can freely download and try ETL tools from Jaspersoft, Pentaho, and Talend that all work withcommunity Cassandra.

/documentation/cql/3.1/cql/cql_reference/copy_r.html

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Troubleshooting

This section contains the following topics:

Peculiar Linux kernel performance problem on NUMA systemsProblems due to zone_reclaim_mode.

The Linux kernel can be inconsistent in enabling/disabling zone_reclaim_mode. This can result in oddperformance problems:

• Random huge CPU spikes resulting in large increases in latency and throughput.• Programs hanging indefinitely apparently doing nothing.• Symptoms appearing and disappearing suddenly.• After a reboot, the symptoms generally do not show again for some time.

To ensure that zone_reclaim_mode is disabled:

$ echo 0 > /proc/sys/vm/zone_reclaim_mode

Reads are getting slower while writes are still fastThe cluster's IO capacity is not enough to handle the write load it is receiving.

Check the SSTable counts in cfstats. If the count is continually growing, the cluster's IO capacity is notenough to handle the write load it is receiving. Reads have slowed down because the data is fragmentedacross many SSTables and compaction is continually running trying to reduce them. Adding more IOcapacity, either via more machines in the cluster, or faster drives such as SSDs, will be necessary to solvethis.

If the SSTable count is relatively low (32 or less) then the amount of file cache available per machinecompared to the amount of data per machine needs to be considered, as well as the application's readpattern. The amount of file cache can be formulated as (TotalMemory – JVMHeapSize) and if theamount of data is greater and the read pattern is approximately random, an equal ratio of reads to thecache:data ratio will need to seek the disk. With spinning media, this is a slow operation. You may beable to mitigate many of the seeks by using a key cache of 100%, and a small amount of row cache(10000-20000) if you have some hot rows and they are not extremely large.

Nodes seem to freeze after some period of timeSome portion of the JVM is being swapped out by the operating system (OS).

Check your system.log for messages from the GCInspector. If the GCInspector is indicating that eitherthe ParNew or ConcurrentMarkSweep collectors took longer than 15 seconds, there is a high probabilitythat some portion of the JVM is being swapped out by the OS.

One way this might happen is if the mmap DiskAccessMode is used without JNA support. The addressspace will be exhausted by mmap, and the OS will decide to swap out some portion of the JVM thatisn't in use, but eventually the JVM will try to GC this space. Adding the JNA libraries will solve this(they cannot be shipped with Cassandra due to carrying a GPL license, but are freely available) or theDiskAccessMode can be switched to mmap_index_only, which as the name implies will only mmap theindices, using much less address space.

DataStax strongly recommends that you disable swap entirely (sudo swapoff --all). BecauseCassandra has multiple replicas and transparent failover, it is preferable for a replica to be killed

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immediately when memory is low rather than go into swap. This allows traffic to be immediately redirectedto a functioning replica instead of continuing to hit the replica that has high latency due to swapping. Ifyour system has a lot of DRAM, swapping still lowers performance significantly because the OS swapsout executable code so that more DRAM is available for caching disks. To make this change permanent,remove all swap file entries from /etc/fstab.

If you insist on using swap, you can set vm.swappiness=1. This allows the kernel swap out the absoluteleast used parts.

If the GCInspector isn't reporting very long GC times, but is reporting moderate times frequently(ConcurrentMarkSweep taking a few seconds very often) then it is likely that the JVM is experiencingextreme GC pressure and will eventually OOM. See the section below on OOM errors.

Nodes are dying with OOM errorsNodes are dying with OutOfMemory exceptions.

Check for these typical causes:

Row cache is too large, or is caching large rows

Row cache is generally a high-end optimization. Try disabling it and see if the OOM problems continue.

The memtable sizes are too large for the amount of heap allocated to the JVM

You can expect N + 2 memtables resident in memory, where N is the number of tables. Adding another1GB on top of that for Cassandra itself is a good estimate of total heap usage.

If none of these seem to apply to your situation, try loading the heap dump in MAT and see which class isconsuming the bulk of the heap for clues.

Nodetool or JMX connections failing on remote nodesNodetool commands can be run locally but not on other nodes in the cluster.

If you can run nodetool commands locally but not on other nodes in the ring, you may have a common JMXconnection problem that is resolved by adding an entry like the following in install_location/conf/cassandra-env.sh on each node:

JVM_OPTS = "$JVM_OPTS -Djava.rmi.server.hostname=<public name>"

If you still cannot run nodetool commands remotely after making this configuration change, do a fullevaluation of your firewall and network security. The nodetool utility communicates through JMX on port7199.

Handling schema disagreementsCheck for and resolve schema disagreements.

About this task

In the event that a schema disagreement occurs, check for and resolve schema disagreements as follows:

Procedure

1. Run the nodetool describecluster command.

$ bin/nodetool describecluster

If any node is UNREACHABLE, you see output something like this:

http://www.eclipse.org/mat/

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$ bin/nodetool describeclusterSnitch: org.apache.cassandra.locator.DynamicEndpointSnitchPartitioner: org.apache.cassandra.dht.Murmur3PartitionerSchema versions: UNREACHABLE: 1176b7ac-8993-395d-85fd-41b89ef49fbb: [10.202.205.203] 9b861925-1a19-057c-ff70-779273e95aa6: [10.80.207.102] 8613985e-c49e-b8f7-57ae-6439e879bb2a: [10.116.138.23]

2. Restart unreachable nodes.

3. Repeat steps 1 and 2 until nodetool describecluster shows that all nodes have the sameschema version number#only one schema version appears in the output.

View of ring differs between some nodesIndicates that the ring is in a bad state.

This situation can happen when not using virtual nodes (vnodes) and there are token conflicts (forinstance, when bootstrapping two nodes simultaneously with automatic token selection.) Unfortunately, theonly way to resolve this is to do a full cluster restart. A rolling restart is insufficient since gossip from nodeswith the bad state will repopulate it on newly booted nodes.

Java reports an error saying there are too many open filesJava may not have open enough file descriptors.

Cassandra generally needs more than the default (1024) amount of file descriptors. To increase thenumber of file descriptors, change the security limits on your Cassandra nodes as described in theRecommended Settings section of Insufficient user resource limits errors.

Another, much less likely possibility, is a file descriptor leak in Cassandra. Run lsof -n | grep javato check that the number of file descriptors opened by Java is reasonable and reports the error if thenumber is greater than a few thousand.

Insufficient user resource limits errorsInsufficient resource limits may result in a number of errors in Cassandra and OpsCenter.

Cassandra errors

Insufficient as (address space) or memlock setting

ERROR [SSTableBatchOpen:1 ] 2012-07-25 15:46:02,913 AbstractCassandraDaemon.java (line 139)Fatal exception in thread Thread [SSTableBatchOpen:1,5,main ]java.io.IOError: java.io.IOException: Map failed at ...

Insufficient memlock settings

WARN [main ] 2011-06-15 09:58:56,861 CLibrary.java (line 118) Unable to lock JVM memory (ENOMEM).This can result in part of the JVM being swapped out, especially with mmapped I/O enabled.Increase RLIMIT_MEMLOCK or run Cassandra as root.

Insufficient nofiles setting

WARN 05:13:43,644 Transport error occurred during acceptance of message.org.apache.thrift.transport.TTransportException: java.net.SocketException:Too many open files ...

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Insufficient nofiles setting

ERROR [MutationStage:11 ] 2012-04-30 09:46:08,102 AbstractCassandraDaemon.java (line 139)Fatal exception in thread Thread [MutationStage:11,5,main ]java.lang.OutOfMemoryError: unable to create new native thread

Recommended settings

You can view the current limits using the ulimit -a command. Although limits can also be temporarilyset using this command, DataStax recommends making the changes permanent:

Packaged installs: Ensure that the following settings are included in the /etc/security/limits.d/cassandra.conf file:

cassandra - memlock unlimitedcassandra - nofile 100000cassandra - nproc 32768cassandra - as unlimited

Tarball installs: Ensure that the following settings are included in the /etc/security/limits.conf file:

* - memlock unlimited* - nofile 100000* - nproc 32768* - as unlimited

If you run Cassandra as root, some Linux distributions such as Ubuntu, require setting the limits for rootexplicitly instead of using *:

root - memlock unlimitedroot - nofile 100000root - nproc 32768root - as unlimited

For CentOS, RHEL, OEL systems, also set the nproc limits in /etc/security/limits.d/90-nproc.conf:

* - nproc 32768

For all installations, add the following line to /etc/sysctl.conf:

vm.max_map_count = 131072

To make the changes take effect, reboot the server or run the following command:

$ sudo sysctl -p

To confirm the limits are applied to the Cassandra process, run the following command where pid is theprocess ID of the currently running Cassandra process:

$ cat /proc/<pid>/limits

OpsCenter errors

See the OpsCenter Troubleshooting documentation.

Cannot initialize class org.xerial.snappy.SnappyAn error may occur when Snappy compression/decompression is enabled although its library is availablefrom the classpath.

java.util.concurrent.ExecutionException: java.lang.NoClassDefFoundError: Could not initialize class org.xerial.snappy.Snappy...

/documentation/opscenter/4.0/opsc/troubleshooting/opscTroubleshooting_g.html

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Caused by: java.lang.NoClassDefFoundError: Could not initialize class org.xerial.snappy.Snappy at org.apache.cassandra.io.compress.SnappyCompressor.initialCompressedBufferLength (SnappyCompressor.java:39)

The native library snappy-1.0.4.1-libsnappyjava.so for Snappy compression is included in thesnappy-java-1.0.4.1.jar file. When the JVM initializes the JAR, the library is added to the defaulttemp directory. If the default temp directory is mounted with a noexec option, it results in the aboveexception.

One solution is to specify a different temp directory that has already been mounted without the noexecoption, as follows:

• If you use the DSE/Cassandra command $_BIN/dse cassandra or $_BIN/cassandra, simplyappend the command line:

• DSE: bin/dse cassandra -t -Dorg.xerial.snappy.tempdir=/path/to/newtmp• Cassandra: bin/cassandra -Dorg.xerial.snappy.tempdir=/path/to/newtmp

• If starting from a package using service dse start or service cassandra start, add a system environmentvariable JVM_OPTS with the value:

JVM_OPTS=-Dorg.xerial.snappy.tempdir=/path/to/newtmp

The default cassandra-env.sh looks for the variable and appends to it when starting the JVM.

Firewall idle connection timeout causing nodes to lose communicationduring low traffic times

About this task

During low traffic intervals, a firewall configured with an idle connection timeout can close connections tolocal nodes and nodes in other data centers. The default idle connection timeout is usually 60 minutes andconfigurable by the network administrator.

Procedure

To prevent connections between nodes from timing out, set the TCP keep alive variables:

1. Get a list of available kernel variables:

$ sysctl -A | grep net.ipv4

The following variables should exist:

• net.ipv4.tcp_keepalive_time

Time of connection inactivity after which the first keep alive request is sent.• net.ipv4.tcp_keepalive_probes

Number of keep alive requests retransmitted before the connection is considered broken.• net.ipv4.tcp_keepalive_intvl

Time interval between keep alive probes.

2. To change these settings:

$ sudo sysctl -w net.ipv4.tcp_keepalive_time=60 net.ipv4.tcp_keepalive_probes=3 net.ipv4.tcp_keepalive_intvl=10

This sample command changes TCP keepalive timeout to 60 seconds with 3 probes, 10 seconds gapbetween each. This setting detects dead TCP connections after 90 seconds (60 + 10 + 10 + 10). There

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is no need to be concerned about the additional traffic as it's negligible and permanently leaving thesesettings shouldn't be an issue.

DataStax Community release notes

214


Key features of Cassandra 2.1 were described earlier in this document. The CHANGES.txt file installedwith Cassandra 2.1 covers changes in detail. Some of the noteworthy changes include:

• Cassandra 2.1 does not support pre-Cassandra 2.0 SSTables.

To upgrade to Cassandra 2.1 from a previous release that stored data in Cassandra 1.2.x SSTables,start the node on Cassandra 2.0 and use the sstableupgrade tool after upgrading. UpgradeSSTables even if you do not perform a rolling upgrade. Resolve schema disagreements if any exist,and restart each node. For more upgrade information, see "Upgrading Cassandra" and NEWS.txt.

• The shuffle utility for migrating to virtual nodes (vnodes) and the nodetool taketoken commandhave been removed. To migrate to vnodes, bootstrap a new data center.

• Cassandra 2.1 bundles and enables JNA. If JNA fails to initialize, you can disable JNA by using the -Dcassandra.boot_without_jna=true option to start Cassandra.

• Cassandra rejects USING TIMESTAMP or USING TTL in the command to update a counter column,and now generates an error message when you attempt such an operation.

• Configurable properties have been added to manage counter writes.• A configurable counter cache reduces lock contention and helps with concurrency.• In Cassandra 2.1, the CQL table property index_interval is replaced by min_index_interval and

max_index_interval. The max_index_interval is 2048 by default. The default would be reached onlywhen SSTables are infrequently-read and the index summary memory pool is full. When upgradingfrom earlier releases, Cassandra uses the old index_interval value for the min_index_interval.

• CASSANDRA-6504 has been backported to Cassandra 2.0.5 so you can perform a rolling upgrade of adatabase having counters to Cassandra 2.1.

• Default data and log locations have changed for tarball installations and source checkouts. By default,the data file directory, commitlog directory, and saved caches directory are in $CASSANDRA_HOME/data/data, $CASSANDRA_HOME/data/commitlog, and $CASSANDRA_HOME/data/saved_caches, respectively. The log directory now defaults to $CASSANDRA_HOME/logs. If not set,$CASSANDRA_HOME, defaults to the top-level directory of the installation. Deb and RPM packagescontinue to use /var/lib/cassandra and /var/log/cassandra by default.

• Cassandra 2.1 maintains data consistency during bootstrapping. As you bootstrap a new node,Cassandra streams the data for the new node from an existing node that is free from range movement.If data inconsistency issues are present in the cluster, the improvement to bootstrapping handles theseissues. Data inconsistency commonly occurs after frequent data deletions and a node going down.

• To inhibit the new Cassandra 2.1 bootstrapping behavior, and make Cassandra 2.0 behavior effective,start the node using the -Dconsistent.rangemovement=false property:

• Package installations: Add the following option to /usr/share/cassandra/cassandra-env.shfile:

JVM_OPTS="$JVM_OPTS -Dconsistent.rangemovement=false• Tarball installations: Start Cassandra with this option:

$ bin/cassandra -Dconsistent.rangemovement=false

To replace a dead node, you also need to specify the address of the node from which Cassandrastreams the data.

For a complete list of fixes and new features, see the Apache Cassandra 2.1.0 CHANGES.txt. You canview all version changes by branch or tag in the branch drop-down list:

https://github.com/apache/cassandra/tree/cassandra-2.1.0

/documentation/upgrade/doc/upgrade/cassandra/upgradeCassandra_g.html

https://github.com/apache/cassandra/blob/cassandra-2.1/NEWS.txt

https://github.com/apache/cassandra/tree/cassandra-2.1.0


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Tips for using DataStax documentation

216

Tips for using DataStax documentation

Navigating the documents

To navigate, use the table of contents or search in the left navigation bar. Additional controls are:

Hide or display the left navigation.

Go back or forward through the topics as listed inthe table of contents.

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Grab to adjust the size of the navigation pane.

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Toggles the legend for CQL statements andnodetool options.

Other resources

You can find more information and help at:

• Documentation home page• Datasheets• Webinars• Whitepapers• Developer blogs• Support

http://www.datastax.com/docs

http://www.datastax.com/resources/datasheets

http://www.datastax.com/resources/webinars

http://www.datastax.com/resources/whitepapers

http://www.datastax.com/dev/blog

http://www.datastax.com/what-we-offer/products-services/support

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Back pressure

Pausing or blocking the buffering of incoming requests after reaching the threshold until the internalprocessing of buffered requests catches up.

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